MAINTAINERS: nx crypto: Fix typo in a filepath

Fix typo in nx_debugfs.c filepath. File extension changed from .h to .c
The file nx_debugfs.h never existed.

Cc: Breno Leitão <leitao@debian.org>
Cc: Nayna Jain <nayna@linux.ibm.com>
Cc: Paulo Flabiano Smorigo <pfsmorigo@gmail.com>
Cc: Dan Streetman <ddstreet@ieee.org>
Cc: Herbert Xu <herbert@gondor.apana.org.au>
Cc: linux-crypto@vger.kernel.org
Signed-off-by: Denis Efremov <efremov@linux.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>