tools: mkeficapsule: resource leak in read_bin_file()

Free the allocated buffer in case of an error.

Fixes: 9e63786e2b4b ("tools: mkeficapsule: rework the code a little bit")
Addresses-Coverity-ID: 345917 Resource leak
Signed-off-by: Heinrich Schuchardt <heinrich.schuchardt@canonical.com>

tools/mkeficapsule.c

@@ -168,6 +168,7 @@ static int read_bin_file(char *bin, uint8_t **data, off_t *bin_size)
 	if (size < bin_stat.st_size) {
 		fprintf(stderr, "read failed (%zx)\n", size);
 		ret = -1;
+		free(buf);
 		goto err;
 	}