Cleanup: zvol_add_clones() should not NULL check dp

It is never NULL because we return early if dsl_pool_hold() fails.

This caused Coverity to complain.

Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: Richard Yao <richard.yao@alumni.stonybrook.edu>
Closes openzfs#14042

module/zfs/zvol.c

@@ -1027,8 +1027,7 @@ zvol_add_clones(const char *dsname, list_t *minors_list)
 out:
 	if (dd != NULL)
 		dsl_dir_rele(dd, FTAG);
-	if (dp != NULL)
-		dsl_pool_rele(dp, FTAG);
+	dsl_pool_rele(dp, FTAG);
 }
 
 /*