[ARM] Fix typo when creating ISD::SUB nodes

[rogfer01]

Summary

In D35192, I accidentally introduced a typo when creating ISD::SUB nodes, giving them two values instead of one.

This fails when the merge_values combiner finds one of these nodes.

[efriedma]

LGTM, but please just use "MVT::i32" explicitly instead of "VT".

[rogfer01]

This blunder of mine caused PR34564.

[rogfer01]

ChangeLog:

• Use MVT::i32 instead of VT