[AArch64] Correct defs and uses on {PAC,AUT}I{A,B}171615 (#123354)

I'm not adding tests for this, as I don't think we usually have tests to
verify correct description of defs and uses in instructions?

This fix will be tested when #122304 lands, as one of the regression
tests in that PR fails without this fix.

llvm/lib/Target/AArch64/AArch64InstrInfo.td

@@ -2030,6 +2030,8 @@ let Predicates = [HasPAuthLR] in {
     //                              opcode2, opcode,   asm
     def AUTIASPPCr : SignAuthOneReg<0b00001, 0b100100, "autiasppcr">;
     def AUTIBSPPCr : SignAuthOneReg<0b00001, 0b100101, "autibsppcr">;
+  }
+  let Defs = [X17], Uses = [X15, X16, X17] in {
     //                                  opcode2, opcode,   asm
     def PACIA171615 : SignAuthFixedRegs<0b00001, 0b100010, "pacia171615">;
     def PACIB171615 : SignAuthFixedRegs<0b00001, 0b100011, "pacib171615">;