iwlwifi: dvm: no need to check return value of debugfs_create functions

When calling debugfs functions, there is no need to ever check the
return value.  This driver was saving the debugfs file away to be
removed at a later time.  However, the 80211 core would delete the whole
directory that the debugfs files are created in, after it asks the
driver to do the deletion, so just rely on the 80211 core to do all of
the cleanup for us, making us not need to keep a pointer to the dentries
around at all.

This cleans up the structure of the driver data a bit and makes the code
a tiny bit smaller.

Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Link: https://lore.kernel.org/r/20190612142658.12792-3-gregkh@linuxfoundation.org
Signed-off-by: Johannes Berg <johannes.berg@intel.com>