[OPENMP]Use the real pointer value as base, not indexed value.

After fix for PR48174 the base pointer for pointer-based
array-sections/array-subscripts will be emitted as `&ptr[idx]`, but
actually it should be just `ptr`, i.e. the address stored in the ponter
to point correctly to the beginning of the array. Currently it may lead
to a crash in the runtime.

Differential Revision: https://reviews.llvm.org/D91805