[PATCH] Fix compiler warning for x86 target

Fix the following compiler warning for x86 target:

sadump_info.c:104:12: warning: 'linux_banner_sanity_check' declared
'static' but never defined [-Wunused-function]
 static int linux_banner_sanity_check(ulong cr3);
              ^

Signed-off-by: Kazuhito Hagio <k-hagio-ab@nec.com>