[lld] Fix R_AVR_7_PCREL and R_AVR_13_PCREL range checking (PR #92695)

[Ben Shi via llvm-commits]

benshi001 wrote:

I agree with the change to `R_AVR_PCREL_7`, there are 7 bits in the `RJMP`/`RCALL` instruction encoding which actually represents [-256, 254].

https://github.com/llvm/llvm-project/pull/92695