Use SET_ERROR for constant non-zero return codes

Update many return and assignment statements to follow the convention
of using the SET_ERROR macro when returning a hard-coded non-zero
value from a function. This aids debugging by recording the error
codes in the debug log.

Reviewed-by: George Melikov <mail@gmelikov.ru>
Reviewed-by: Giuseppe Di Natale <dinatale2@llnl.gov>
Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Reviewed by: Matthew Ahrens <mahrens@delphix.com>
Signed-off-by: Ned Bass <bass6@llnl.gov>
Closes #6441

module/zfs/arc.c

@@ -6187,7 +6187,7 @@ arc_kstat_update(kstat_t *ksp, int rw)
 	arc_stats_t *as = ksp->ks_data;
 
 	if (rw == KSTAT_WRITE) {
-		return (EACCES);
+		return (SET_ERROR(EACCES));
 	} else {
 		arc_kstat_update_state(arc_anon,
 		    &as->arcstat_anon_size,