[IA64] Fix a possible buffer overflow in efi.c

Make sure to save space for the trailing '\0'.

Signed-off-by: Zou Nan hai <[e-mail]>
Signed-off-by: Tony Luck <[e-mail]>

arch/ia64/kernel/efi.c

···
 	/* Show what we know for posterity */
 	c16 = __va(efi.systab->fw_vendor);
 	if (c16) {
-		for (i = 0;i < (int) sizeof(vendor) && *c16; ++i)
+		for (i = 0;i < (int) sizeof(vendor) - 1 && *c16; ++i)
 			vendor[i] = *c16++;
 		vendor[i] = '\0';
 	}