util/broadcom: Check return value of stat()

Change-Id: Ib53408e8b186c07aa8e42c67131d39c4add05983
Signed-off-by: Patrick Georgi <pgeorgi@chromium.org>
Found-by: Coverity Scan #1323515
Reviewed-on: https://review.coreboot.org/17881
Tested-by: build bot (Jenkins)
Reviewed-by: Martin Roth <martinroth@google.com>

util/broadcom/secimage/sbi.c

@@ -109,7 +109,10 @@ int CreateSecureBootImage(int ac, char **av)
 		--ac, ++av;
 	}
 
-	stat(bl, &file_stat);
+	if (stat(bl, &file_stat) == -1) {
+		puts("Can't stat bl");
+		return -1;
+	}
 	filesize = file_stat.st_size + MIN_SIZE;
 	buf = calloc(sizeof(uint8_t), filesize);