mips: kernel: no need to check return value of debugfs_create functions

When calling debugfs functions, there is no need to ever check the
return value.  The function can work or not, but the code logic should
never do something different based on this.

Cc: Ralf Baechle <ralf@linux-mips.org>
Cc: Paul Burton <paul.burton@mips.com>
Cc: James Hogan <jhogan@kernel.org>
Cc: Yangtao Li <tiny.windzz@gmail.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Mike Rapoport <rppt@linux.vnet.ibm.com>
Cc: Mathieu Malaterre <malat@debian.org>
Cc: Huacai Chen <chenhc@lemote.com>
Cc: Marcin Nowakowski <marcin.nowakowski@mips.com>
Cc: Yasha Cherikovsky <yasha.che3@gmail.com>
Cc: linux-mips@vger.kernel.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Paul Burton <paul.burton@mips.com>