btrfs: remove unnecessary NULL fs_info check from find_lock_delalloc_range()

btrfs: remove unnecessary NULL fs_info check from find_lock_delalloc_range()

[STATIC CHECK REPORT]
Smatch is reporting that find_lock_delalloc_range() used to do a null
pointer check before accessing fs_info, but now we're accessing it for
sectorsize unconditionally.

[FALSE ALERT]
This is a false alert, the existing null pointer check is introduced in
commit f7b12a62f008 ("btrfs: replace BTRFS_MAX_EXTENT_SIZE with
fs_info->max_extent_size"), but way before that, commit 7c0260ee098d
("btrfs: tests, require fs_info for root") is already forcing every
btrfs_root to have a correct fs_info pointer.

So there is no way that btrfs_root::fs_info is NULL.

[FIX]
Just remove the unnecessary NULL pointer checker.

Reported-by: kernel test robot <lkp@intel.com>
Reported-by: Dan Carpenter <dan.carpenter@linaro.org>
Fixes: f7b12a62f008 ("btrfs: replace BTRFS_MAX_EXTENT_SIZE with fs_info->max_extent_size")
Closes: https://lore.kernel.org/r/202509250925.4L4JQTtn-lkp@intel.com/
Signed-off-by: Qu Wenruo <wqu@suse.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>