Fix getters for register with only wo fields
ioreg: No need to read from write-only registers
ioreg/parser: Nightly fallout
platformtree: Prefer indexing to _.get()
Merge pull request #145 from bgamari/ioreg-write-only

ioreg: write-only register fixes
Merge pull request #142 from bgamari/master

Nightly fallout
Merge pull request #128 from bgamari/ioreg-test

Add rudimentary tests for ioreg
ioreg/test: Add test for #140

write-only registers shouldn't be read from.