ARM: pxa: magician: Optimize Samsung LCD refresh to 50Hz

Change the default Samsung LCD refresh from an unrealistic 117Hz to 50Hz
as no video applications on the HTC Magician can work that fast.

The optimalization lowers the RAM latency at least by 3%.

Signed-off-by: Petr Cvek <petr.cvek@tul.cz>
Acked-by: Philipp Zabel <philipp.zabel@gmail.com>
Signed-off-by: Robert Jarzmik <robert.jarzmik@free.fr>