linux/modules/mmap_file: support kernels without debugfs
linux/modules/mmap_file: support kernels without debugfs

When CONFIG_DEBUG_FS is not enabled, debugfs_create_file_unsafe() is not
declared and debugfs_create_file() is defined as a stub returning
ERR_PTR(-ENODEV). Implement the code which is needed in order to handle
this case correctly.

fishilico/shared,fishilico/shared,fishilico/shared,fishilico/shared,fishilico/shared,fishilico/shared,fishilico/shared