drm/bridge: anx7625: Propagate errors from sp_tx_rst_aux()

The return value of sp_tx_rst_aux() is not propagated, which means
both compiler warnings and potential errors not being handled.

Fixes: 8bdfc5da

 ("drm/bridge: anx7625: Add anx7625 MIPI DSI/DPI to DP")

Reviewed-by: Sam Ravnborg <sam@ravnborg.org>
Reported-by: kernel test robot <lkp@intel.com>
Signed-off-by: Robert Foss <robert.foss@linaro.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20210818171318.1848272-1-robert.foss@linaro.org