spmi: use more appropriate name for spmi devices

Using a pointer for the name makes devices near impossible to access
from sysfs reliably without an alias. Change this to either use the
unique of_node name or the of_node name and the device's address.

Signed-off-by: Bjorn Andersson <bjorn.andersson@sonymobile.com>
Merge pull request #9 from andersson/for-alin/spmi-non-random-names

spmi: use more appropriate name for spmi devices