[lld] [lld][ELF] Fix a corner case of elf::getLoongArchPageDelta (PR #71907)

[via llvm-commits]

heiher wrote:

Another corner case?

DEST: 0 PC: 0x80000ffc

```
80000ffc: 05 00 00 1b  	pcalau12i	$a1, -524288
80001000: 04 00 c0 02  	addi.d	$a0, $zero, 0
80001004: e4 ff ff 17  	lu32i.d	$a0, -1
80001008: 84 fc 3f 03  	lu52i.d	$a0, $a0, -1
8000100c: 84 94 10 00  	add.d	$a0, $a0, $a1
```

https://github.com/llvm/llvm-project/pull/71907