x86: fix buffer overflow in efi_init()

If the vendor name (from c16) can be longer than 100 bytes (or missing a
terminating null), then the null is written past the end of vendor[].

Found with Parfait, http://research.sun.com/projects/parfait/



Signed-off-by: Roel Kluin <roel.kluin@gmail.com>
Cc: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: H. Peter Anvin <hpa@zytor.com>
Cc: Huang Ying <ying.huang@intel.com>