coccinelle: ignore_return.cocci: Update script
coccinelle: ignore_return.cocci: Update script

* Provide a single liner description at top using `///`
  comments. This one liner is displayed when using `--verbose`
  mode of coccicheck.

* Specify Condidence level property adhering to coccinelle.rst
  section "Proposing new semantic patches".

* Add virtual patch rule to handle the patch case when coccicheck
  is supplied with `--mode=patch` option.

* Add `depends on !(file in "ext")` to ignore reports from `ext/`
  directory.

* Simplify patch rule to reduce effort in reconstruction since
  logically we are only *adding* void cast.

Signed-off-by: Himanshu Jha <db39123178a3996d9dafcdcc9af59c3e841de70a@gmail.com>

GiulianoFranchetto/zephyr,ldts/zephyr,galak/zephyr,punitvara/zephyr,finikorg/zephyr,ldts/zephyr,punitvara/zephyr,Vudentz/zephyr,ldts/zephyr,nashif/zephyr,Vudentz/zephyr,GiulianoFranchetto/zephyr,galak/zephyr,nashif/zephyr,galak/zephyr,explora26/zephyr,Vudentz/zephyr,finikorg/zephyr,ldts/zephyr,Vudentz/zephyr,punitvara/zephyr,zephyrproject-rtos/zephyr,explora26/zephyr,nashif/zephyr,punitvara/zephyr,finikorg/zephyr,nashif/zephyr,finikorg/zephyr,GiulianoFranchetto/zephyr,punitvara/zephyr,galak/zephyr,zephyrproject-rtos/zephyr,zephyrproject-rtos/zephyr,explora26/zephyr,finikorg/zephyr,zephyrproject-rtos/zephyr,ldts/zephyr,Vudentz/zephyr,explora26/zephyr,zephyrproject-rtos/zephyr,explora26/zephyr,GiulianoFranchetto/zephyr,GiulianoFranchetto/zephyr,nashif/zephyr,galak/zephyr,Vudentz/zephyr