vfio-ccw: make vfio_ccw_async_region_ops static

Since vfio_ccw_async_region_ops is not exported and has no reason to be
globally visible make it static to avoid the following sparse warning:
drivers/s390/cio/vfio_ccw_async.c:73:30: warning: symbol 'vfio_ccw_async_region_ops' was not declared. Should it be static?

Fixes: d5afd5d135c8 ("vfio-ccw: add handling for async channel instructions")
Reviewed-by: Cornelia Huck <[e-mail]>
Signed-off-by: Vasily Gorbik <[e-mail]>

drivers/s390/cio/vfio_ccw_async.c

···
 
 }
 
-const struct vfio_ccw_regops vfio_ccw_async_region_ops = {
+static const struct vfio_ccw_regops vfio_ccw_async_region_ops = {
 	.read = vfio_ccw_async_region_read,
 	.write = vfio_ccw_async_region_write,
 	.release = vfio_ccw_async_region_release,