drm/msm/dsi: fix error checks and return values for DSI xmit functions

drm/msm/dsi: fix error checks and return values for DSI xmit functions

As noticed by Dan ([1] an the followup thread) there are multiple issues
with the return values for MSM DSI command transmission callback. In
the error case it can easily return a positive value when it should
have returned a proper error code.

This commits attempts to fix these issues both in TX and in RX paths.

[1]: https://lore.kernel.org/linux-arm-msm/20211001123617.GH2283@kili/

Fixes: a689554ba6ed ("drm/msm: Initial add DSI connector support")
Reported-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>
Reviewed-by: Abhinav Kumar <quic_abhinavk@quicinc.com>
Tested-by: Marijn Suijten <marijn.suijten@somainline.org>
Patchwork: https://patchwork.freedesktop.org/patch/480501/
Link: https://lore.kernel.org/r/20220401231104.967193-1-dmitry.baryshkov@linaro.org
Signed-off-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>