[RISCV] Remove earlyclobber from compares with LMUL<=1.

Compares are considered a narrowing operation for register overlap.
I believe for LMUL<=1 they meet this exception to allow overlap

"The destination EEW is smaller than the source EEW and the overlap is in the
lowest-numbered part of the source register group"

Both the result and the sources will occupy a single register for
LMUL<=1 so the overlap would always be in the "lowest-numbered part".

Reviewed By: frasercrmck, HsiangKai

Differential Revision: https://reviews.llvm.org/D103336