Fix IP520 pointer cast warnings

[JJL772]

Luckily this is RTEMS-only code, and all of our supported RTEMS targets are 32-bit. Regardless, converting int -> ptr is a bad idea, especially without an explicit cast. Incompatible function pointers are even worse, but will still work in this case.

../ip520_RTEMS.c: In function 'IP520ModuleInit':
../ip520_RTEMS.c:403:9: warning: passing argument 4 of 'ipmIntConnect' from incompatible pointer type [enabled by default]
         if (ipmIntConnect(carrier, slot, int_num, IP520Int, IP520LastModule))
         ^
In file included from ../ip520_RTEMS.c:45:0:
../../include/drvIpac.h:224:20: note: expected 'void (*)(void *)' but argument is of type 'void (*)(int)'
 epicsShareFunc int ipmIntConnect(int carrier, int slot, int vector, 
                    ^
../ip520_RTEMS.c:403:9: warning: passing argument 5 of 'ipmIntConnect' makes pointer from integer without a cast [enabled by default]
         if (ipmIntConnect(carrier, slot, int_num, IP520Int, IP520LastModule))
         ^
In file included from ../ip520_RTEMS.c:45:0: