ext4: move out inode_lock into ext4_fallocate()

Currently, all five sub-functions of ext4_fallocate() acquire the
inode's i_rwsem at the beginning and release it before exiting. This
process can be simplified by factoring out the management of i_rwsem
into the ext4_fallocate() function.

Signed-off-by: Zhang Yi <yi.zhang@huawei.com>
Reviewed-by: Jan Kara <jack@suse.cz>
Reviewed-by: Ojaswin Mujoo <ojaswin@linux.ibm.com>
Link: https://patch.msgid.link/20241220011637.1157197-10-yi.zhang@huaweicloud.com


Signed-off-by: Theodore Ts'o <tytso@mit.edu>