[DAGCombiner] Move or/xor/and opcode check in ReduceLoadOpStoreWidth before hasOneUse check.

hasOneUse is not cheap on nodes with chain results that might have
many uses. By checking the opcode first, we can avoid a costly walk
of the use list on nodes we aren't interested in.

Found by investigating calls to hasNUsesOfValue from the example
provided in D123857.