arm: tcc8k: Avoid reading clock register twice

There is no reason why in case of PLL2 the configuration register
should be read twice, while for PLL0/1 using the value previously read
is used. Do the same for PLL2.

Signed-off-by: Oskar Schirmer <oskar@linutronix.de>
Cc: bigeasy@linutronix.de
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>