cel.c: Fix mismatch in ast_cel_track_event() return type.

The return type of ast_cel_track_event() is not large enough to return all
64 potential bits of the event enable mask.  Fortunately, the defined CEL
events do not really need all 64 bits and the return value is only used to
determine if the requested CEL event is enabled.

* Made the ast_cel_track_event() return 0 or 1 only so the return value
can fit inside an int type instead of zero or a truncated 64 bit non-zero
value.

Change-Id: I783d932320db11a95c7bf7636a72b6fe2566904c