drivers/video/nuc900fb.c: fix lcd build error

Fix a nuc900 lcd build error.

Since the 'nuc900_driver_clksrc_div()' API cannot be merged into mainline
successfully, I removed this clock source selection hook in this driver.
This means nuc900 lcd driver has to select default clock source from the
external crystal now.

Signed-off-by: Wan ZongShun <mcuos.com@gmail.com>
Cc: Qiang Wang <rurality.wq@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>