drivers/spi-rockchip.c : Remove redundant variable slave

variable slave in spi_alloc_master() or spi_alloc_slave()
has been assigned. it is not necessary to be assigned again

Signed-off-by: Lizhe <sensor1010@163.com>
Link: https://lore.kernel.org/r/20230226063334.7489-1-sensor1010@163.com


Signed-off-by: Mark Brown <broonie@kernel.org>