callers of iov_copy_from_user_atomic() don't need pagecache_disable()

commit 9e8c2af9 upstream.

... it does that itself (via kmap_atomic())

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: Mel Gorman <mgorman@suse.de>
Signed-off-by: Jiri Slaby <jslaby@suse.cz>