Fix uninitialized value read in vdev_prop_set()

If no errors are encountered, we read an uninitialized error value.

Clang's static analyzer complained about this.

Reviewed-by: Tino Reichardt <milky-zfs@mcmilk.de>
Reviewed-by: Ryan Moeller <ryan@iXsystems.com>
Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: Richard Yao <richard.yao@alumni.stonybrook.edu>
Closes #14007

module/zfs/vdev.c

@@ -5648,7 +5648,7 @@ vdev_prop_set(vdev_t *vd, nvlist_t *innvl, nvlist_t *outnvl)
 	nvpair_t *elem = NULL;
 	uint64_t vdev_guid;
 	nvlist_t *nvprops;
-	int error;
+	int error = 0;
 
 	ASSERT(vd != NULL);