drm/vboxvideo: use managed pci functions

drm/vboxvideo: use managed pci functions

Allows us to drop the cleanup code on the floor.

Sam noticed in his review:
> With this change we avoid calling pci_disable_device()
> twise in case vbox_mm_init() fails.
> Once in vbox_hw_fini() and once in the error path.

v2: Include Sam's review remarks

v3: Fix typo in commit summary (Thomas Zimmermann)

Acked-by: Sam Ravnborg <[email protected]>
Reviewed-by: Hans de Goede <[email protected]>
Signed-off-by: Daniel Vetter <[email protected]>
Cc: Hans de Goede <[email protected]>
Link: https://patchwork.freedesktop.org/patch/msgid/[email protected]