audio/csound: fix build with clang 18

With clang 18, audio/csound fails to build:

/wrkdirs/usr/ports/audio/csound/work/csound-6.15.0/Opcodes/OSC.c:784:47: error: incompatible function pointer types passing 'int32_t (const char *, const char *, lo_arg , int32_t, void *, void *)' (aka 'int (const char *, const char *, lo_arg , int, void *, void *)') to parameter of type 'lo_method_handler' (aka 'int (*)(const char *, const char *, lo_arg **, int, struct lo_message_ *, void *)') [-Wincompatible-function-pointer-types]

784 |                                               OSC_handler, p->port);
    |                                               ^~~~~~~~~~~

/usr/local/include/lo/lo_serverthread.h:151:72: note: passing argument to parameter 'h' here

151 |                                const char *typespec, lo_method_handler h,
    |                                                                        ^

This is because the callback functions OSC_handler() and OSC_ahandler()
have the wrong signature: liblo's headers use 'int' for the 'argc'
argument, and 'lo_message' for the 'data' argument. Fix the parameter
types of the functions to match the liblo declarations.

PR: 277999
Approved by: maintainer timeout (2 weeks)
MFH: 2024Q2