tools include: Adopt ERR_CAST() from the kernel err.h header

Add ERR_CAST(), so that tools can use it, just like the kernel.

This addresses coccinelle checks that are being performed to tools/ in
addition to kernel sources, so lets add this to cover that and to get
tools code closer to kernel coding standards.

This originally was introduced in the kernel headers in this cset:

  d1bc8e95 ("Add an ERR_CAST() function to complement ERR_PTR and co.")

Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: David Ahern <dsahern@gmail.com>
Cc: David Howells <dhowells@redhat.com>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Julia Lawall <julia.lawall@lip6.fr>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Wang Nan <wangnan0@huawei.com>
Cc: Wen Yang <yellowriver2010@hotmail.com>
Cc: zhong.weidong@zte.com.cn
Link: https://lkml.kernel.org/n/tip-tlt97p066zyhzqhl5jt86og7@git.kernel.org


Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>