serial: 8250_pxa: avoid autodetecting the port type

serial: 8250_pxa: avoid autodetecting the port type

If we're unlucky enough that this drivers binds to a mrvl,mmp-uart device
on a MMP3, the port type gets detected as 16550A instead of XScale, and it
won't work. Other drivers that may bind to the same hardware are 8250_of
and, god forbid, serial_pxa.

Force the port type, we know it's a PORT_XSCALE.

Signed-off-by: Lubomir Rintel <lkundrak@v3.sk>
Link: https://lore.kernel.org/r/20200219080130.4334-1-lkundrak@v3.sk
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>