[PowerPC] Another folow-up fix for 6c4b40de

There was another issue introduced by this commit that the OP
initially missed. Namely, for functions that are free to use
R2 as a callee-saved register, we emit a TOC expression based
on the address of the GEP label without emitting the GEP label.
Since we only emit such expressions for the large code model, this
issue only surfaced there.

I have confirmed that with this fix, the kernel build is successful
with target "all".