Add missing *_destroy/*_fini calls

The proposed debugging enhancements in zfsonlinux/spl#587
identified the following missing *_destroy/*_fini calls.

Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: Gvozden Neskovic <neskovic@gmail.com>
Closes #5428

cmd/raidz_test/raidz_test.c

@@ -729,6 +729,8 @@ exit:
 		    (ulong_t)tried_comb);
 	}
 
+	mutex_destroy(&sem_mtx);
+
 	return (sweep_state == SWEEP_ERROR ? SWEEP_ERROR : 0);
 }