Call nvlist_free before return

Fixes a small kernel memory leak which would occur if a pool failed
to import because the `DMU_POOL_VDEV_ZAP_MAP` key can't be read from 
a presumably damaged MOS config.  In the case of a missing key there 
was no leak.

Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Reviewed-by: Ryan Moeller <ryan@iXsystems.com>
Signed-off-by: Finix1979 <yancw@info2soft.com>
Closes openzfs#13629

module/zfs/spa.c

@@ -4211,6 +4211,7 @@ spa_ld_get_props(spa_t *spa)
 		spa->spa_avz_action = AVZ_ACTION_INITIALIZE;
 		ASSERT0(vdev_count_verify_zaps(spa->spa_root_vdev));
 	} else if (error != 0) {
+		nvlist_free(mos_config);
 		return (spa_vdev_err(rvd, VDEV_AUX_CORRUPT_DATA, EIO));
 	} else if (!nvlist_exists(mos_config, ZPOOL_CONFIG_HAS_PER_VDEV_ZAPS)) {
 		/*