selftests/livepatch: use TEST_PROGS for test scripts

Adrian reports that 'make -C tools clean' results in removal of the
livepatch selftest shell scripts.

As per the selftest lib.mk file, TEST_PROGS are for test shell scripts,
not TEST_GEN_PROGS.  Adjust the livepatch selftest Makefile accordingly.

Reported-by: Adrian Hunter <adrian.hunter@intel.com>
Signed-off-by: Joe Lawrence <joe.lawrence@redhat.com>
Tested-by: Adrian Hunter <adrian.hunter@intel.com>
Signed-off-by: Petr Mladek <pmladek@suse.com>