There is no need to keep the dentries around for the individual debugfs
files, just delete the whole directory all at once at shutdown instead.

This also fixes a tiny memory leak where the memory for the pointers to
the file dentries was never freed when the device shut down, as well as
making the logic of the code a lot simpler.
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Bartlomiej Zolnierkiewicz <b.zolnierkie@samsung.com>