serial: 8250_dw: Hide a cast in dw8250_serial_inq()

dw8250_serial_inq() uses unsigned int variable to store 8-bit value.
Due to that it needs a cast which can be avoided by switching to use
u8 instead of unsigned int.

Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Link: https://lore.kernel.org/r/20240412173937.187442-1-andriy.shevchenko@linux.intel.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>