serial: 8250_exar: Replace msleep(1) with usleep_range()

As explained in Documentation/timers/timers-howto.rst
the small amount of milliseconds sometimes produces
much longer delays.

Replace msleep(1) with usleep_range(1000, 1100).

Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Link: https://lore.kernel.org/r/20190805142535.21948-2-andriy.shevchenko@linux.intel.com


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