gpio: qcom_pmic: fix silent dev_read_addr downcast

priv->pid is uint32_t, but dev_read_addr() returns a uint64_t on arm64,
with the upper bits being used for error codes. Do error checking before
downcasting to u32 to prevent errors being silently ignored.

Reviewed-by: Sumit Garg <sumit.garg@linaro.org>
Reviewed-by: Neil Armstrong <neil.armstrong@linaro.org>
Tested-by: Sumit Garg <sumit.garg@linaro.org>
Reviewed-by: Simon Glass <sjg@chromium.org>
Signed-off-by: Caleb Connolly <caleb.connolly@linaro.org>