[Flang][HLFIR] Relax size check for dot_product intrinsic

If the size of one of the operand arrays is not known at compile
time, do not issue a size mismatch error sinc they could match at
runtime.

Fixes the compilation error in polyhedron/induct2.

Reviewed By: tblah, vzakhari

Differential Revision: https://reviews.llvm.org/D155302