[ELF] Simplify findOrphanPos. NFC

Simplify the loop that considers sections of the same proximity. The two
involved conditions are due to:

* https://reviews.llvm.org/D111717 ("[ELF] Avoid adding an orphan section to a less suitable segment") and
* https://reviews.llvm.org/D112925 ("[ELF] Better resemble GNU ld when placing orphan sections into memory regions")