tty: serial: 8250: Fix line continuation warning

Fixed checkpatch warning about an unnecessary line continuation in a
multi-line variable assignment.

Signed-off-by: Anton Würfel <anton.wuerfel@fau.de>
Signed-off-by: Phillip Raffeck <phillip.raffeck@fau.de>
Reviewed-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Reviewed-by: Peter Hurley <peter@hurleysoftware.com>
Cc: linux-kernel@i4.cs.fau.de
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>