GlobalISel: Remove faulty assert in buildAtomicRMW op

Vectors are supported for fp operations now, so remove the assert. The
supported type/operation combinations are best left for the verifier.
Avoids regression in future commit that starts treating some vector
cases as legal.

Author: arsenm

llvm/lib/CodeGen/GlobalISel/MachineIRBuilder.cpp

@@ -996,7 +996,6 @@ MachineInstrBuilder MachineIRBuilder::buildAtomicRMW(
   LLT OldValResTy = OldValRes.getLLTTy(*getMRI());
   LLT AddrTy = Addr.getLLTTy(*getMRI());
   LLT ValTy = Val.getLLTTy(*getMRI());
-  assert(OldValResTy.isScalar() && "invalid operand type");
   assert(AddrTy.isPointer() && "invalid operand type");
   assert(ValTy.isValid() && "invalid operand type");
   assert(OldValResTy == ValTy && "type mismatch");