The two functions cpm_muram_offset() and cpm_muram_dma() both need a
cast currently, one casts muram_vbase to do the pointer arithmetic on
void pointers, the other casts the passed-in address u8*.

It's simpler and more consistent to just always use void* and drop all
the casting.

Signed-off-by: Rasmus Villemoes <rasmus.villemoes@prevas.dk>
Acked-by: Li Yang <leoyang.li@nxp.com>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>