misc: fastrpc: Add dma_mask to fastrpc_channel_ctx

dma_set_mask_and_coherent only updates the mask to which the device
dma_mask pointer points to. Add a dma_mask to the channel ctx and set
the device dma_mask to point to that, otherwise the dma_set_mask will
return an error and the dma_set_coherent_mask will be skipped too.

Co-developed-by: Srinivas Kandagatla <srinivas.kandagatla@linaro.org>
Signed-off-by: Abel Vesa <abel.vesa@linaro.org>
Signed-off-by: Srinivas Kandagatla <srinivas.kandagatla@linaro.org>
Link: https://lore.kernel.org/r/20221125071405.148786-11-srinivas.kandagatla@linaro.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>