hypervisor: Fix cleaning of generated files for latest kernels

Recent kernels seem to add their own prefix to clean-files, thus won't
remove our files as the paths gets wrong. We can simply remove $(obj),
that works both for current and older kernels.

Signed-off-by: Jan Kiszka <jan.kiszka@siemens.com>

hypervisor/Makefile

@@ -55,8 +55,8 @@ define filechk_version
 	$(src)/../scripts/gen_version_h $(src)/..
 endef
 
-clean-files := $(obj)/include/jailhouse/config.mk \
-	$(obj)/include/jailhouse/version.h
+clean-files := include/jailhouse/config.mk \
+	include/jailhouse/version.h
 
 define sed-y
 	"/^=>/{s:=>#\(.*\):/* \1 */:; \