serial: pmac_zilog: add sparse context annotation

serial: pmac_zilog: add sparse context annotation

Add sparse context annotation to the receive handler, which releases and
reacquires the port lock, to silence a sparse warning:

	drivers/tty/serial/pmac_zilog.c:255:36: sparse: sparse: context imbalance in 'pmz_receive_chars' - unexpected unlock

Reported-by: kernel test robot <lkp@intel.com>
Signed-off-by: Johan Hovold <johan@kernel.org>
Reviewed-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Link: https://lore.kernel.org/r/20200723123327.5843-2-johan@kernel.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>