[SLP] Skip MMRA metadata if instruction can't have it (#173319)
Exposed by recent commit in e644f06c2ffc, but the wrong propagation
might be applied in other situations too.
Without this, we will get verification errors with e644f06c2ffc.
!mmra metadata attached to unexpected instruction kind
%3 = fmul <2 x float> %2, <float 1.000000e+00, float 0.000000e+00>,
!mmra !1