BUILD: Silence gcc warning about unused return value

BUILD: Silence gcc warning about unused return value

gcc (Ubuntu 5.4.0-6ubuntu1~16.04.11) 5.4.0 20160609
Copyright (C) 2015 Free Software Foundation, Inc.
This is free software; see the source for copying conditions.  There is NO
warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.

complains:

> src/debug.c: In function "ha_panic":
> src/debug.c:162:2: warning: ignoring return value of "write", declared with attribute warn_unused_result [-Wunused-result]
>  (void) write(2, trash.area, trash.data);
>    ^