ntfs: drop stale page-cache when shrinking a non-resident attr

ntfs: drop stale page-cache when shrinking a non-resident attr

ntfs_non_resident_attr_shrink() shrinks attribute sizes but fails to
trim the page cache. This leaves orphaned dirty folios beyond the new
end of the attribute, leading to writeback failures (-ENOENT), data
loss, and $EA chain corruption.

Fix this by truncating the page cache to the new size immediately after
updating the sizes, preventing writeback from flushing out-of-range folios.

Fixes: 495e90fa3348 ("ntfs: update attrib operations")
Signed-off-by: Namjae Jeon <linkinjeon@kernel.org>