buffer: Remove calls to set and clear the folio error flag

The folio error flag is not tested anywhere, so we can stop setting
and clearing it.

Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Link: https://lore.kernel.org/r/20240530202110.2653630-17-willy@infradead.org


Signed-off-by: Christian Brauner <brauner@kernel.org>