drm/bridge: anx7625: Fix null vs IS_ERR() checking in anx7625_register_i2c_dummy_clients

drm/bridge: anx7625: Fix null vs IS_ERR() checking in anx7625_register_i2c_dummy_clients

Since i2c_new_client_device() function return error pointers.
The i2c_new_dummy_device() function does not return NULL, It returns error
pointers too. Using IS_ERR() to check the return value to fix this.

Fixes: 8bdfc5dae4e3("drm/bridge: anx7625: Add anx7625 MIPI DSI/DPI to DP")
Signed-off-by: Miaoqian Lin <linmq006@gmail.com>
Signed-off-by: Robert Foss <robert.foss@linaro.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20211222083350.18514-1-linmq006@gmail.com
Reviewed-by: Robert Foss <robert.foss@linaro.org>