x86, kaslr: Use char array to gain sizeof sanity

The build_str needs to be char [] not char * for the sizeof() to report
the string length.

Reported-by: Mathias Krause <minipli@googlemail.com>
Signed-off-by: Kees Cook <keescook@chromium.org>
Link: http://lkml.kernel.org/r/20131112165607.GA5921@www.outflux.net
Signed-off-by: H. Peter Anvin <hpa@zytor.com>

arch/x86/boot/compressed/aslr.c

@@ -13,7 +13,7 @@
 #include <linux/version.h>
 
 /* Simplified build-specific string for starting entropy. */
-static const char *build_str = UTS_RELEASE " (" LINUX_COMPILE_BY "@"
+static const char build_str[] = UTS_RELEASE " (" LINUX_COMPILE_BY "@"
 		LINUX_COMPILE_HOST ") (" LINUX_COMPILER ") " UTS_VERSION;
 
 #define I8254_PORT_CONTROL	0x43