atyfb: reorganize clock init

Reorganize atyfb clock init code so command line clock overrides are effective
for all chips.  The old code would silently ignore some of the command line
clock overrides with some chips.

Signed-off-by: Antonino Daplas <adaplas@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>