[SLP] Use the correct identity when combining binary opcodes with AND/MUL (#180457)
Fixes #180456
Fix bug in the following SLP lowering:
```
define void @sub_mul(ptr %p, ptr %s) {
entry:
%p1 = getelementptr i16, ptr %p, i64 1
%l0 = load i16, ptr %p
%l1 = load i16, ptr %p1
%mul0 = sub i16 %l0, 0
%mul1 = mul i16 %l1, 5
%s1 = getelementptr i16, ptr %s, i64 1
store i16 %mul0, ptr %s
store i16 %mul1, ptr %s1
ret void
}
```
to
```
define void @sub_mul(ptr %p, ptr %s) {
entry:
%tmp0 = load <2 x i16>, ptr %p, align 2
%tmp1 = mul <2 x i16> %tmp0, <i16 0, i16 5> -> updates to <i16 1, i16 5>
store <2 x i16> %tmp1, ptr %s, align 2
ret void
}
```
95ef1a5c31