selftest/lkdtm: Don't pollute 'git status'

Commit 46d1a0f0 ("selftests/lkdtm: Add tests for LKDTM targets")
added generation of lkdtm test scripts.

Ignore those generated scripts when performing 'git status'

Fixes: 46d1a0f0 ("selftests/lkdtm: Add tests for LKDTM targets")
Signed-off-by: Christophe Leroy <christophe.leroy@c-s.fr>
Signed-off-by: Shuah Khan <skhan@linuxfoundation.org>