[InstCombine] Fix type mismatch in `foldBitmaskMul` (#199920)
Resolves #199506.
`matchBitmaskMul` matches the form `!(A & N) ? 0 : N * C`.
When the select arms are splat vectors but A is a scalar, this produces
malformed ir like `%57 = and i64 %49, <4 x i64> splat (i64
3689348814741910323)`.
Reproducer: https://godbolt.org/z/EYzKTxcKn