staging: sm750fb: merge calcPLL and getPllValue into getChipClock

The getChipClock function is used only to get MXCLK frequency, which
makes most of getPllValue function unused and thus. The detection of
MXCLK frequency may be implemented directly in getChipClock rendering
getPllValue and calcPLL unused.

Signed-off-by: Mike Rapoport <mike.rapoport@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>