fix kernel modules build after updating linux to v5.9.2

- `dep.c` and `dep2.c`: `debugfs_create_u32` does not return anymore, not
  sure why:
  https://unix.stackexchange.com/questions/593983/creating-a-debugfs-file-that-is-used-to-read-write-u32-value/621282#621282
  So just doing `debugfs_lookup` for now
- vermagic.c:
  51161bfc66
  prevents its usage in v5.8. Just migrating to `init_utsname` for now
- procfs.c: `struct file_operations` moved to a new `struct proc_ops` at:
  b567e07513
- myprintk.c: `pr_warning` dropped for `pr_warn`:
  61ff72f401
- `poll.c`: `kthread_func` is not defined in kernel, prefix with lkmc to
  avoid conflict

Fix https://github.com/cirosantilli/linux-kernel-module-cheat/issues/136

Fix https://github.com/cirosantilli/linux-kernel-module-cheat/issues/137

kernel_modules/vermagic.c

@@ -2,11 +2,34 @@
 
 #include <linux/module.h>
 #include <linux/kernel.h>
-#include <linux/vermagic.h>
+#include <linux/utsname.h>
+#if 0
+#include <linux/vermagic.h> /* VERMAGIC_STRING */
+#endif
 
 static int myinit(void)
 {
+    struct new_utsname *uts = init_utsname();
+	pr_info(
+        "sysname    = %s\n"
+        "nodename   = %s\n"
+        "release    = %s\n"
+        "version    = %s\n"
+        "machine    = %s\n"
+        "domainname = %s\n",
+        uts->sysname,
+        uts->nodename,
+        uts->release,
+        uts->version,
+        uts->machine,
+        uts->domainname
+    );
+
+#if 0
+    /* Possible before v5.8, but was buggy apparently, not sure why:
+     * https://github.com/cirosantilli/linux/commit/51161bfc66a68d21f13d15a689b3ea7980457790 */
 	pr_info("VERMAGIC_STRING = " VERMAGIC_STRING "\n");
+#endif
 	/* Nice try, but it is not a member. */
 	/*pr_info("THIS_MODULE->vermagic = %s\n", THIS_MODULE->vermagic);*/
 	return 0;