fix incompatible pointer type warning

Fixes the following warning:

kpatch-patch-hook.c:71:2: warning: initialization from incompatible pointer type [enabled by default]
  __ATTR(enabled, 0644, patch_enabled_show, patch_enabled_store);
  ^

Signed-off-by: Seth Jennings <sjenning@redhat.com>
Merge pull request #182 from spartacus06/fix-warning

fix incompatible pointer type warning