clk: mmp2: Fix the display clock divider base

clk: mmp2: Fix the display clock divider base

The LCD clock dividers are apparently based on one. No datasheet,
determined empirically, but seems to be confirmed by line 19 of lcd.fth in
OLPC laptop's Open Firmware [1]:

   h# 00000700 value pmua-disp-clk-sel  \ PLL1 / 7 -> 113.86 MHz

[1] https://raw.githubusercontent.com/quozl/openfirmware/65a08a73b2cac/cpu/arm/olpc/lcd.fth

Signed-off-by: Lubomir Rintel <lkundrak@v3.sk>
Link: https://lore.kernel.org/r/20200925233914.227786-1-lkundrak@v3.sk
Signed-off-by: Stephen Boyd <sboyd@kernel.org>