meson: fix incorrect substitutions in configured files

The custom Makefile rules performed this substitution:

@@var@@ -> VAL

However, meson did this substitution:

@@var@@ -> @Val@

This produced incorrect behavior, such as configuring a udev file to
read:

install_items+=" @/usr/etc/udev/rules.d@/70-nvmf-autoconnect.rules "

muon, meanwhile, failed loudly with:

/tmp/nvme-cli/nvmf-autoconnect/dracut-conf/70-nvmf-autoconnect.conf.in:1:19: error: key of zero length not supported
  1 | install_items+=" @@UDEVRULESDIR@@/70-nvmf-autoconnect.rules "
                        ^
/tmp/nvme-cli/meson.build:161:1: error: in function configure_file
161 | configure_file(
      ^

Since meson does not support custom token rules for configuring
replacements, and there is no real benefit to doubling the @@, just fix
this to use one @.

Makefile

@@ -222,11 +222,11 @@ install-spec: install-bin install-man install-bash-completion install-zsh-comple
 install: install-spec install-hostparams
 
 nvme.spec: nvme.spec.in NVME-VERSION-FILE
-	sed -e 's/@@VERSION@@/$(NVME_VERSION)/g' < $< > $@+
+	sed -e 's/@VERSION@/$(NVME_VERSION)/g' < $< > $@+
 	mv $@+ $@
 
 70-nvmf-autoconnect.conf: nvmf-autoconnect/dracut-conf/70-nvmf-autoconnect.conf.in
-	sed -e 's#@@UDEVRULESDIR@@#$(UDEVRULESDIR)#g' < $< > $@+
+	sed -e 's#@UDEVRULESDIR@#$(UDEVRULESDIR)#g' < $< > $@+
 	mv $@+ $@
 
 dist: nvme.spec
@@ -236,9 +236,9 @@ dist: nvme.spec
 	gzip -f -9 nvme-$(NVME_VERSION).tar
 
 control: nvme.control.in NVME-VERSION-FILE
-	sed -e 's/@@VERSION@@/$(NVME_VERSION)/g' < $< > $@+
+	sed -e 's/@VERSION@/$(NVME_VERSION)/g' < $< > $@+
 	mv $@+ $@
-	sed -e 's/@@DEPENDS@@/$(LIB_DEPENDS)/g' < $@ > $@+
+	sed -e 's/@DEPENDS@/$(LIB_DEPENDS)/g' < $@ > $@+
 	mv $@+ $@
 
 pkg: control nvme.control.in

nvme.control.in

@@ -1,9 +1,9 @@
 Package: nvme
-Version: @@VERSION@@
+Version: @VERSION@
 Section: base
 Priority: optional
 Architecture: amd64
-Depends: @@DEPENDS@@
+Depends: @DEPENDS@
 Maintainer: Keith Busch <kbusch@kernel.org>
 Description: NVM-Express Command Line Interface
  The nvme management tool

nvme.spec.in

@@ -1,11 +1,11 @@
 Name: 		nvme
-Version: 	@@VERSION@@
+Version: 	@VERSION@
 Release: 	1%{?dist}
 Summary:  	Core nvme tools
 License: 	GPL
 Group: 		Development/Tools
 URL: 		https://github.com/linux-nvme/nvme-cli/
-Source: 	nvme-@@VERSION@@.tar.gz
+Source: 	nvme-@VERSION@.tar.gz
 Provides:	nvme
 Requires(post): util-linux systemd systemd-udev
 BuildRoot:	%{_tmppath}/%{name}-%{version}-root

nvmf-autoconnect/dracut-conf/70-nvmf-autoconnect.conf.in

@@ -1 +1 @@
-install_items+=" @@UDEVRULESDIR@@/70-nvmf-autoconnect.rules "
+install_items+=" @UDEVRULESDIR@/70-nvmf-autoconnect.rules "