[LV] Don't assume isScalarAfterVectorization if one of the uses needs widening.

This fixes an issue that was found in D105199, where a GEP instruction
is used both as the address of a store, as well as the value of a store.
For the former, the value is scalar after vectorization, but the latter
(as value) requires widening.

Other code in that function seems to prevent similar cases from happening,
but it seems this case was missed.

Reviewed By: david-arm

Differential Revision: https://reviews.llvm.org/D106164