[AArch64][NFC] Normalise name of indexed forms of SQRDMLAH/SQRDMLSH

Most indexed vector instructions are suffixed with v<N><TY>_indexed.

SQRDMLAH/SQRDMLSH are the exception, being suffixed with <TY>_indexed
instead, which can complicate matching them slightly.

Differential Revision: https://reviews.llvm.org/D152161