arch-arm: Fix format specifier in encodeAArch64SysReg panic

The panic was using the wrong format specifier: %n instead of %d

Change-Id: I92f0be85dc24da06373cba5c20bab6de7d7b4537
Signed-off-by: Giacomo Travaglini <giacomo.travaglini@arm.com>
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/60729
Reviewed-by: Richard Cooper <richard.cooper@arm.com>
Maintainer: Andreas Sandberg <andreas.sandberg@arm.com>
Tested-by: kokoro <noreply+kokoro@google.com>
Reviewed-by: Andreas Sandberg <andreas.sandberg@arm.com>

src/arch/arm/regs/misc.cc

@@ -1317,7 +1317,7 @@ encodeAArch64SysReg(MiscRegIndex misc_reg)
         it != idxToMiscRegNum.end()) {
         return it->second;
     } else {
-        panic("Invalid MiscRegIndex: %n\n", misc_reg);
+        panic("Invalid MiscRegIndex: %d\n", misc_reg);
     }
 }