Fix use of uninitialised variable.

The RK805 regs array was being allocated before it's required size was
known, causing the driver to use memory it didn't own. That memory
was subsequently allocated and used elsewhere causing later fatal data
aborts in rk805_map().

Whilst I'm here, add a sanity check to catch unsupported PMICs (this
shouldn't ever get hit because the probe should have failed).

Reviewed by: manu
MFC after: 1 week
Sponsored by: Google