Misc: Fix more Clang warnings in core and darwin

* http://sourceforge.net/mailarchive/message.php?msg_id=29418038
* core.c:700:4: warning: Function call argument is an uninitialized value
* darwin_usb.c:1713:11: warning: Access to field 'cfSource' results in a
  dereference of a null pointer (loaded from variable 'hpriv')
* sync.c/dpfp.c/dpfp_threaded.c: warning: Result of 'malloc' is converted
  to a pointer of type 'unsigned char', which is incompatible with sizeof
  operand type