Add a helper that takes a virtual address rather than the muram
offset. This will be used in a couple of places to avoid having to
store both the offset and the virtual address, as well as removing
NULL checks from the callers.

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>