get_user_pages() may return fewer page than we ask for.  As we give up and
return an error in this case, we need to put_page() each of the pages we
did get.

[Andy Walls modified the patch, only removing the braces in the 'for'
statement, to eliminate a checkpatch warning.]
Signed-off-by: Paul Cassella <fortytwo-ivtv@manetheren.bigw.org>
Signed-off-by: Andy Walls <awalls@md.metrocast.net>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>