tty: xilinx_uartps: Initialise the read_status_mask

Initialise the read status in probe.
It will be checked in the isr so to have the default values lets initialise
in probe.

Signed-off-by: Shubhrajyoti Datta <shubhrajyoti.datta@xilinx.com>
Link: https://lore.kernel.org/r/20220729114748.18332-4-shubhrajyoti.datta@xilinx.com


Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>