There is no multi_write support available if we cannot use raw_write.
This is the case if bus->write is not implemented.

This patch adds a condition that we need bus and bus->write so that
can_multi_write is true.
Signed-off-by: NMarkus Pargmann <mpa@pengutronix.de>
Signed-off-by: NMark Brown <broonie@kernel.org>