x86, mrst: A function in a header file needs to be marked "inline"

A function in a header file needs to be explicitly marked "inline", or
gcc will complain if it is not used.

Signed-off-by: H. Peter Anvin <hpa@linux.intel.com>
Cc: Jacob Pan <jacob.jun.pan@linux.intel.com>
Cc: <stable@kernel.org> v2.6.36
LKML-Reference: <1274295685-6774-3-git-send-email-jacob.jun.pan@linux.intel.com>