tty: serial: altera_jtaguart: use uart_port::read_status_mask

tty: serial: altera_jtaguart: use uart_port::read_status_mask

Instead of self-defined struct altera_jtaguart::imr, use preexisting
uart_port::read_status_mask.

Note that imr was ulong. But there is no reason for that, its values are
uints. And readl/writel's are used to read it/write to it.

Cc: Tobias Klauser <tklauser@distanz.ch>
Signed-off-by: Jiri Slaby (SUSE) <jirislaby@kernel.org>
Reviewed-by: Tobias Klauser <tklauser@distanz.ch>
Link: https://lore.kernel.org/r/20221115071724.5185-3-jirislaby@kernel.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>