mic: Remove unneeded NULL check

debugfs_remove_recursive will do NULL check, so remove
the redundant null check.

Signed-off-by: Xu Wang <vulab@iscas.ac.cn>
Reviewed-by: Ashutosh Dixit <ashutosh.dixit@intel.com>
Link: https://lore.kernel.org/r/1578391235-603-1-git-send-email-vulab@iscas.ac.cn


Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>