writeback: merge try_to_writeback_inodes_sb_nr() into caller

Since commit 925a6efb8ff0c ("Btrfs: stop using
try_to_writeback_inodes_sb_nr to flush delalloc") this function hasn't
been used outside so stop exporting it.

In addition we merge it into try_to_writeback_inodes_sb() which is the
only caller.  Also change return type of try_to_writeback_inodes_sb to
void as the only user ext4 doesn't care.

Reviewed-by: Jan Kara <jack@suse.cz>
Signed-off-by: Rakesh Pandit <rakesh@tuxera.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
diff --git a/include/linux/writeback.h b/include/linux/writeback.h
index dd1d2c2..e15ec14 100644
--- a/include/linux/writeback.h
+++ b/include/linux/writeback.h
@@ -163,9 +163,7 @@ struct bdi_writeback;
 void writeback_inodes_sb(struct super_block *, enum wb_reason reason);
 void writeback_inodes_sb_nr(struct super_block *, unsigned long nr,
 							enum wb_reason reason);
-bool try_to_writeback_inodes_sb(struct super_block *, enum wb_reason reason);
-bool try_to_writeback_inodes_sb_nr(struct super_block *, unsigned long nr,
-				   enum wb_reason reason);
+void try_to_writeback_inodes_sb(struct super_block *sb, enum wb_reason reason);
 void sync_inodes_sb(struct super_block *);
 void wakeup_flusher_threads(enum wb_reason reason);
 void wakeup_flusher_threads_bdi(struct backing_dev_info *bdi,