test_kmod: stop kernel-doc warnings

Use kernel-doc notation to prevent warnings:

lib/test_kmod.c:58: warning: contents before sections
lib/test_kmod.c:94: warning: cannot understand function prototype: 'struct kmod_test_device_info '
lib/test_kmod.c:119: warning: cannot understand function prototype: 'struct kmod_test_device '

Signed-off-by: Randy Dunlap <rdunlap@infradead.org>
Cc: Luis Chamberlain <mcgrof@kernel.org>
Cc: linux-modules@vger.kernel.org
Signed-off-by: Luis Chamberlain <mcgrof@kernel.org>