[LSR] Canonicalize a formula before insert it into the list

In GenerateConstantOffsetsImpl, we may generate non canonical Formula
if BaseRegs of that Formula is updated and includes a recurrent expr reg
related with current loop while its ScaledReg is not.

Patched by: mdchen
Reviewed By: qcolombet

Differential Revision: https://reviews.llvm.org/D86939