afs: Unlock pages for __pagevec_release()

[ Upstream commit 21bd68f196ca91fc0f3d9bd1b32f6e530e8c1c88 ]

__pagevec_release() complains loudly if any page in the vector is still
locked.  The pages need to be locked for generic_error_remove_page(), but
that function doesn't actually unlock them.

Unlock the pages afterwards.

Signed-off-by: Marc Dionne <marc.dionne@auristor.com>
Signed-off-by: David Howells <dhowells@redhat.com>
Tested-by: Jonathan Billings <jsbillin@umich.edu>
Signed-off-by: Sasha Levin <sashal@kernel.org>