ext4: remove redundant check buffer_uptodate()

Now set_buffer_uptodate() will test first and then set, so we don't have
to check buffer_uptodate() first, remove it to simplify code.

Reviewed-by: Ritesh Harjani <riteshh@linux.ibm.com>
Signed-off-by: Joseph Qi <joseph.qi@linux.alibaba.com>
Link: https://lore.kernel.org/r/1619418587-5580-1-git-send-email-joseph.qi@linux.alibaba.com
Signed-off-by: Theodore Ts'o <tytso@mit.edu>