ext4: fix trimmed block count accunting

Currently when there is not enough free blocks in the block group to
discard (grp->bb_free < minlen) the 'trimmed' is bumped up anyway with
the number of discarded blocks from the previous iteration. Fix this
by bumping up 'trimmed' only if the ext4_trim_all_free() was actually
run.
Signed-off-by: Lukas Czerner <lczerner@redhat.com>
Reviewed-by: Jan Kara <jack@suse.cz>
Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>

fs/ext4/mballoc.c

@@ -5026,8 +5026,8 @@ int ext4_trim_fs(struct super_block *sb, struct fstrim_range *range)
 				ret = cnt;
 				break;
 			}
+			trimmed += cnt;
 		}
-		trimmed += cnt;
 
 		/*
 		 * For every group except the first one, we are sure