efivars: memory leak on error in create_efivars_bin_attributes()

This is a cut and paste bug.  We intended to free ->del_var and
->new_var but we only free ->new_var.

Signed-off-by: Dan Carpenter <error27@gmail.com>
Acked-by: Mike Waychison <mikew@google.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>