HID: samples/hidraw: add .gitignore file

To fix:

 # Untracked files:
 #   (use "git add <file>..." to include in what will be committed)
 #
 #	samples/hidraw/hid-example

as seen in git status output after an allyesconfig build.

Signed-off-by: Paul Gortmaker <paul.gortmaker@windriver.com>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>