opaque_master: Use new API to register shutdown function

This allows opaque masters to register shutdown function in
opaque_master struct, which means there is no need to call
register_shutdown in init function, since this call is now a part
of register_opaque_master.

As a consequence of using new API, two things are happening here:
1) No resource leakage anymore in case register_shutdown() would fail,
2) Fixed propagation of register_opaque_master() return values.

BUG=b:185191942
TEST=1) builds and ninja test including CB:56413
2) on ARMv7 device
flashrom -p linux_mtd -V
-> using linux_mtd, chip found

Change-Id: Id8471a117556edcbf9694752fabe05cf4501ce70
Signed-off-by: Anastasia Klimchuk <aklm@chromium.org>
Reviewed-on: https://review.coreboot.org/c/flashrom/+/56825
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Edward O'Callaghan <quasisec@chromium.org>

linux_mtd.c

@@ -314,6 +314,7 @@ static const struct opaque_master linux_mtd_opaque_master = {
 	.read		= linux_mtd_read,
 	.write		= linux_mtd_write,
 	.erase		= linux_mtd_erase,
+	.shutdown	= linux_mtd_shutdown,
 };
 
 /* Returns 0 if setup is successful, non-zero to indicate error */
@@ -418,14 +419,7 @@ static int linux_mtd_init(void)
 		return 1;
 	}
 
-	if (register_shutdown(linux_mtd_shutdown, (void *)data)) {
-		free(data);
-		return 1;
-	}
-
-	register_opaque_master(&linux_mtd_opaque_master, data);
-
-	return 0;
+	return register_opaque_master(&linux_mtd_opaque_master, data);
 
 linux_mtd_init_exit:
 	free(param);