ARM: 6778/1: compressed/head.S: make LDFLAGS_vmlinux into a recursively expanded variable

The simply expanded variable may be evaluated before the target file for
the stat command is up to date or even exists.  Switching to a recursively
expanded variable move the execution of the stat command to the location
where LDFLAGS_vmlinux is actually used, fixing the dependency issue
introduced by patch #6746/1.
Signed-off-by: Nicolas Pitre <nicolas.pitre@linaro.org>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>

arch/arm/boot/compressed/Makefile

@@ -84,7 +84,7 @@ EXTRA_CFLAGS  := -fpic -fno-builtin
 EXTRA_AFLAGS  := -Wa,-march=all
 
 # Provide size of uncompressed kernel to the decompressor via a linker symbol.
-LDFLAGS_vmlinux := --defsym _image_size=$(shell stat -c "%s" $(obj)/../Image)
+LDFLAGS_vmlinux = --defsym _image_size=$(shell stat -c "%s" $(obj)/../Image)
 # Supply ZRELADDR to the decompressor via a linker symbol.
 ifneq ($(CONFIG_AUTO_ZRELADDR),y)
 LDFLAGS_vmlinux += --defsym zreladdr=$(ZRELADDR)