It is unnecessary to disable preemption explicitly while calling
copy_highpage().  Because copy_highpage() will do it again through
kmap_atomic/kunmap_atomic.
Signed-off-by: Akinobu Mita <akinobu.mita@gmail.com>
Reviewed-by: Thomas Hellstrom <thellstrom@vmware.com>
Signed-off-by: Dave Airlie <airlied@redhat.com>