ir3: Don't count (nopX) towards the wrong category

Prior to this commit

(nop3) mad.f32 r0.y, c0.x, r1.w, c0.y

was counted as 4 cat3 instructions (and still 3 cat0/nops) in shader-db results. With this change, it is counted as only 1 cat3 instruction.

Probably never going to have better shader-db results than this in my career:

total cat2 in shared programs: 1214667 -> 732058 (-39.73%)
cat2 in affected programs: 1194729 -> 712120 (-40.39%)
helped: 8551
HURT: 0

total cat3 in shared programs: 376448 -> 274745 (-27.02%)
cat3 in affected programs: 344918 -> 243215 (-29.49%)
helped: 7222
HURT: 0