Callers are generally not supposed to check the return values from
debugfs functions.  Debugfs functions never return NULL so this error
handling will never trigger.  (Historically debugfs functions used to
return a mix of NULL and error pointers but it was eventually deemed too
complicated for something which wasn't intended to be used in normal
situations).

Delete all the error handling.
Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Acked-by: Santosh Shilimkar <ssantosh@kernel.org>
Link: https://lore.kernel.org/r/20200826113759.GF393664@mwandaSigned-off-by: Krzysztof Kozlowski <krzk@kernel.org>