serial: 8250_pci: remove redundant assignment to tmp after the mask operation

The variable tmp is being masked with a bitmask and the value is being
written to port base + 0x3c.  However, the masked value is being written
back to tmp and tmp is never used after this. The assignmentment is
redundant, replace the &= operator with just &.

Signed-off-by: Colin Ian King <colin.i.king@gmail.com>
Reviewesd-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Link: https://lore.kernel.org/r/20211205232822.110099-1-colin.i.king@gmail.com


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