tty: serial: qcom_geni_serial: Use u32 for register variables

Use u32 rather than unsigned long for register variables for clarity and
consistency.

Signed-off-by: Ryan Case <ryandcase@chromium.org>
Reviewed-by: Stephen Boyd <swboyd@chromium.org>
Reviewed-by: Evan Green <evgreen@chromium.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>