hwdb: check that uppercase digits are used in modalias patterns

This is all confusing as hell, becuase in some places lowercase hexadecimal
digits are used, and in other places uppercase. This adds a check for the
most common case that we and others got wrong.

I tried to extend the general grammar in hwdb_grammar() to include this check,
but it quickly became very complicated and didn't seem to work properly. Doing
initial parsing with more general rules is easier and also seems to give better
error messages:

/home/zbyszek/src/systemd-work/build/../hwdb.d/60-autosuspend.hwdb: 3 match groups, 5 matches, 3 properties
Pattern 'v058fp9540*' is invalid: Expected W:(0123...), found 'f'  (at char 4), (line:1, col:5)