[LegalizeTypes][NVPTX] Remove extra compare from fallback code for ISD::ADD in Expand...

[LegalizeTypes][NVPTX] Remove extra compare from fallback code for ISD::ADD in ExpandIntRes_ADDSUB.

This is the ultimate fallback code if UADDO isn't supported.

If the target uses 0/1 we used one compare, but if the target doesn't
use 0/1 we emitted two compares. Regardless of boolean constants we
should only need to check that the Result is less than one of the
original operands. So we only need one compare.

Reviewed By: spatel

Differential Revision: https://reviews.llvm.org/D133708