ppc/p4080: Fix mask width of RCW fields MEM_PLL_RAT, SYS_PLL_RAT

The masks for MEM_PLL_RAT and SYS_PLL_RAT should have been 5-bits
instead of 4.

Signed-off-by: James Yang <James.Yang@freescale.com>
Signed-off-by: Kumar Gala <galak@kernel.crashing.org>