clk: at91: clk-master: remove dead code

Commit facb87ad ("clk: at91: sama7g5: remove prescaler part of master
clock") removed the master clock's prescaler from clock tree of SAMA7G5
as it has been discovered that there is a hardware bug when trying to
change it at run-time (bug is described in description of
commit facb87ad ("clk: at91: sama7g5: remove prescaler part of master
clock")). This was previously changed at CPUFreq driver request. Thus, with
commit facb87ad ("clk: at91: sama7g5: remove prescaler part of master
clock") there is no need of code that handles run-time changes of master
clock's prescaler, thus remove this code.

Signed-off-by: Claudiu Beznea <claudiu.beznea@microchip.com>
Signed-off-by: Nicolas Ferre <nicolas.ferre@microchip.com>
Link: https://lore.kernel.org/r/20220203110202.18329-1-claudiu.beznea@microchip.com