[Hexagon] Fix inner CONCAT_VECTORS type in combineConcatOfScalarPreds (#191756)
The inner CONCAT_VECTORS result type was hardcoded to MVT::v8i1, which
is only correct when BitBytes == 1. Otherwise, the inner concat produces
fewer elements than 8, causing an assertion failure:
Assertion `(Ops[0].getValueType().getVectorElementCount() * Ops.size())
== VT.getVectorElementCount() && "Incorrect element count in vector
concatenation!"' failed.
Fix by computing the inner vector type dynamically based on BitBytes.