serial: 8250_dw: Fix the trivial typo in the comment

Fix the trivial typo in the comment: Premilinary --> Preliminary.

Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Link: https://lore.kernel.org/r/20211005134529.23256-2-andriy.shevchenko@linux.intel.com


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