fbdev: i.MX31: fix panning, error handling, clean up

fbdev: i.MX31: fix panning, error handling, clean up

1. check for errors returned from clk_get()
2. fix "Unbalanced enable for IRQ 160"
3. fix transmit descriptor handling in panning
4. clean frame buffer on blank - useful for OLED displays
5. formatting clean up

Signed-off-by: Guennadi Liakhovetski <[email protected]>
Cc: Dan Williams <[email protected]>
Cc: Sascha Hauer <[email protected]>
Cc: Krzysztof Helt <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>