UPSTREAM: spi: rockchip: check requesting dma channel with EPROBE_DEFER

UPSTREAM: spi: rockchip: check requesting dma channel with EPROBE_DEFER

Let's defer probing the driver if the return value of
dma_request_slave_channel is ERR_PTR(-EPROBE_DEFER) instead
of disabling dma capability directly.

Change-Id: I8371178a772cd310df711d7d3b5fe5288be5000d
Signed-off-by: Shawn Lin <shawn.lin@rock-chips.com>
Signed-off-by: Mark Brown <broonie@kernel.org>
Signed-off-by: Caesar Wang <wxt@rock-chips.com>
(cherry picked from git.kernel.org next/linux-next.git master
 commit 61cadcf46cfdb9f7eec70527968c2b91e9823786)