Fix compilation on gcc 12.2.0

[Quentin01]

Hi,

When compiling on gcc 12.2.0 (default version on Debian bookworm), this error occurs:

In file included from capstone/arch/ARM/../../include/capstone/capstone.h:296,
                 from capstone/arch/ARM/../../Mapping.h:11,
                 from capstone/arch/ARM/ARMInstPrinter.c:32:
capstone/arch/ARM/../../include/capstone/arm.h: In function ‘ARMVPTPredToString’:
capstone/arch/ARM/../../include/capstone/arm.h:159:1: error: control reaches end of non-void function [-Werror=return-type]
  159 | }
      | ^
cc1: all warnings being treated as errors

This PR fix the error.

I could have fixed it with a __builtin_unreachable but it isn't available on MSVC. The assert & the fact that the switch above should handle all valid values of the enum should be enough to prevent issues anyway.

[Rot127]

Can't test it currently. But LGTM.

[kabeor]

Thx, merged.