fuse: keep inode->i_blkbits constant

fuse: keep inode->i_blkbits constant

With fuse now using iomap for writeback handling, inode blkbits changes
are problematic because iomap relies on inode->i_blkbits for its
internal bitmap logic. Currently we change inode->i_blkbits in fuse to
match the attr->blksize value passed in by the server.

This commit keeps inode->i_blkbits constant in fuse. Any attr->blksize
values passed in by the server will not update inode->i_blkbits. The
client-side behavior for stat is unaffected, stat will still reflect the
blocksize passed in by the server.

Signed-off-by: Joanne Koong <joannelkoong@gmail.com>
Link: https://lore.kernel.org/20250807175015.515192-1-joannelkoong@gmail.com
Fixes: ef7e7cbb32 ("fuse: use iomap for writeback")
Signed-off-by: Christian Brauner <brauner@kernel.org>