fix f_count description in Documentation/filesystems/files.txt

Documentation/filesystems/files.txt was not updated when
f_count became an atomic_long_t.
atomic_long_inc_not_zero() is now used instead of atomic_inc_not_zero()

Signed-off-by: Al Viro <[e-mail]>

Documentation/filesystems/files.txt

···
 5. Handling of the file structures is special. Since the look-up
    of the fd (fget()/fget_light()) are lock-free, it is possible
    that look-up may race with the last put() operation on the
-   file structure. This is avoided using atomic_inc_not_zero()
+   file structure. This is avoided using atomic_long_inc_not_zero()
    on ->f_count :
 
 	rcu_read_lock();
 	file = fcheck_files(files, fd);
 	if (file) {
-		if (atomic_inc_not_zero(&file->f_count))
+		if (atomic_long_inc_not_zero(&file->f_count))
 			*fput_needed = 1;
 		else
 		/* Didn't get the reference, someone's freed */
···
 	....
 	return file;
 
-   atomic_inc_not_zero() detects if refcounts is already zero or
+   atomic_long_inc_not_zero() detects if refcounts is already zero or
    goes to zero during increment. If it does, we fail
    fget()/fget_light().