serial: 8250: Do not set UART_LSR_THRE in @read_status_mask

serial: 8250: Do not set UART_LSR_THRE in @read_status_mask

Since Linux 2.1.8 @read_status_mask is no longer used as a
general control of which bits are used from the LSR register.
Instead it has become an additional mask applied to
@ignore_status_mask. Since UART_LSR_THRE is never set for
@ignore_status_mask, it serves no purpose to set it for
@read_status_mask. In fact, it propagates the misconception
that @read_status_mask can be used as a general mask for LSR
bits.

Do not set UART_LSR_THRE for @read_status_mask.

Signed-off-by: John Ogness <john.ogness@linutronix.de>
Link: https://lore.kernel.org/r/20241216171244.12783-3-john.ogness@linutronix.de
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>