Annotated dprintf as printf-like

ZFS loves using %llu for uint64_t, but that requires a cast to not 
be noisy - which is even done in many, though not all, places.
Also a couple places used %u for uint64_t, which were promoted
to %llu. 

Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: Rich Ercolani <rincebrain@gmail.com>
Closes #12233

module/zfs/dsl_destroy.c

@@ -654,7 +654,7 @@ dsl_destroy_snapshots_nvl(nvlist_t *snaps, boolean_t defer,
 		char *errorstr = NULL;
 		(void) nvlist_lookup_string(result, ZCP_RET_ERROR, &errorstr);
 		if (errorstr != NULL) {
-			zfs_dbgmsg(errorstr);
+			zfs_dbgmsg("%s", errorstr);
 		}
 		fnvlist_free(wrapper);
 		fnvlist_free(result);