folio_queue: fix documentation

s/folioq_count/folioq_full/

Reported-by: Stephen Rothwell <sfr@canb.auug.org.au>
Link: https://lore.kernel.org/r/20241001134729.3f65ae78@canb.auug.org.au


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