CVE-2026-90259

In the Linux kernel, the following vulnerability has been resolved:

btrfs: qgroup: fix a wrong length calculation in qgroup_free_reserved_data()

In that function, we round down the start position and round up the
ending position.

But during the calculation of @len, we use "round_up(start + len,
sectorsize)", which is the rounded up end position, not the rounded up
length.

Which results a much larger length, and later we are still using
"start + len", which is completely incorrect.

Fix it by declaring a local @aligned_start and @aligned_len and use them
instead.