checkout_merged(): squelch false warning from some gcc

gcc 4.6.2 (there may be others) does not realize that the variable "mode"
can never be used uninitialized in this function and issues a false warning
under -Wuninitialized option.

Squelch it with an unnecessary initialization; it is not like a single
assignment matters to the performance in this codepath that writes out
to the filesystem with checkout_entry() anyway.

Signed-off-by: Junio C Hamano <gitster@pobox.com>

builtin/checkout.c

@@ -152,7 +152,7 @@ static int checkout_merged(int pos, struct checkout *state)
 	unsigned char sha1[20];
 	mmbuffer_t result_buf;
 	unsigned char threeway[3][20];
-	unsigned mode;
+	unsigned mode = 0;
 
 	memset(threeway, 0, sizeof(threeway));
 	while (pos < active_nr) {