vfio: platform: simplify device removal

vfio_platform_remove_common() cannot return non-NULL in
vfio_amba_remove() as the latter is only called if vfio_amba_probe()
returned success.

Diagnosed-by: Arnd Bergmann <arnd@arndb.de>
Acked-by: Eric Auger <eric.auger@redhat.com>
Link: https://lore.kernel.org/r/20210126165835.687514-4-u.kleine-koenig@pengutronix.de


Signed-off-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>