ARM: 8244/1: fbdev: sa1100fb: make use of device clock

Use per-device clock (instead of calling cpufreq_get(0), which can
return 0 if no cpu frequency driver is selected) to program timings.

Signed-off-by: Dmitry Eremin-Solenikov <dbaryshkov@gmail.com>
Acked-by: Tomi Valkeinen <tomi.valkeinen@ti.com>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>