[AVR] Remove earlyclobber from LDDRdPtrQ (#85277)

LDDRdPtrQ was marked as `earlyclobber`, which doesn't play well with
GreedyRA (which can generate this instruction through `loadRegFromStackSlot()`).

This seems to be the same case as:

https://github.com/llvm/llvm-project/blob/a99b912c9b74f6ef91786b4dfbc25160c27d3b41/llvm/lib/Target/AVR/AVRInstrInfo.td#L1421

Closes https://github.com/llvm/llvm-project/issues/81911.