media: uvcvideo: Fix uvc_alloc_entity() allocation alignment

The use of ALIGN() in uvc_alloc_entity() is incorrect, since the size of
(entity->pads) is not a power of two. As a stop-gap, until a better
solution is adapted, use roundup() instead.

Found by a static assertion. Compile-tested only.

Fixes: 4ffc2d89 ("uvcvideo: Register subdevices for each entity")

Signed-off-by: Nadav Amit <namit@vmware.com>
Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org>