Commit c71a77ab8 (ns16550: switch to resource) has introduced generic
read/write access to 16550 register and a 'shift' parameter to allign
register index to physicall registers.
The correct 'shift' value was missing in all omap based boards.
Corrected this to 2 which has fixed the problem.

Tested on a PCM-049 phyCORE-OMAP4 board.

Signed-off-by: Juergen Kilb <J.Kilb@phytec.de>
Tested-by: Jan Weitzel <J.Weitzel@phytec.de>
Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>