Declare the major number for wd, so that a custom kernel can specific explicit root on wd0a.
Declare the major number for wd, so that a custom kernel can specific explicit
root on wd0a.

Problem spotted by Denis A. Doroshenko.

orumin/openbsd-efivars,orumin/openbsd-efivars,orumin/openbsd-efivars,orumin/openbsd-efivars