Fix build for mingw32 on windows ($$ expansion)

Make using mingw32 on windows fails when running grep "=y$$".
The command is expanded to grep "=y$ and the missing "
results in an error.

I don't expect a file config-devices.mak with =y somewhere in
the middle of a line (they are always at the end of the line),
so simplifying the regular expression to =y seems to be permitted.

This avoids problems with wrong expansion.

Signed-off-by: Stefan Weil <weil@mail.berlios.de>
Signed-off-by: Anthony Liguori <aliguori@us.ibm.com>

Makefile

@@ -39,7 +39,7 @@ SUBDIR_MAKEFLAGS=$(if $(V),,--no-print-directory)
 SUBDIR_DEVICES_MAK=$(patsubst %, %/config-devices.mak, $(TARGET_DIRS))
 
 config-all-devices.mak: $(SUBDIR_DEVICES_MAK)
-	$(call quiet-command,cat $(SUBDIR_DEVICES_MAK) | grep "=y$$" | sort -u > $@,"  GEN   $@")
+	$(call quiet-command,cat $(SUBDIR_DEVICES_MAK) | grep =y | sort -u > $@,"  GEN   $@")
 
 %/config-devices.mak: default-configs/%.mak
 	$(call quiet-command,cat $< > $@.tmp, "  GEN   $@")