vboxsf: Convert vboxsf_read_folio() to use a folio

vboxsf: Convert vboxsf_read_folio() to use a folio

Remove conversion to a page and use folio APIs throughout.  This includes
a removal of setting the error flag as nobody checks the error flag on
vboxsf folios.  This does not include large folio support as we would
have to map each page individually.

Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Link: https://lore.kernel.org/r/20240530202110.2653630-15-willy@infradead.org
Tested-by: Hans de Goede <hdegoede@redhat.com>
Reviewed-by: Hans de Goede <hdegoede@redhat.com>
Signed-off-by: Christian Brauner <brauner@kernel.org>