rdp-compositor: fix compilation against FreeRDP 2.0.0 rc2

The SURFACE_BITS_COMMAND struct has changed and some members have been moved in the
bmp field.

Reviewed-by: Pekka Paalanen <pekka.paalanen@collabora.co.uk>
Tested-by: Pekka Paalanen <pekka.paalanen@collabora.co.uk>