crypto: qat - remove check after debugfs_create_dir()

The debugfs functions are guaranteed to return a valid error code
instead of NULL upon failure. Consequently, the driver can directly
propagate any error returned without additional checks.

Remove the unnecessary `if` statement after debugfs_create_dir(). If
this function fails, the error code is stored in accel_dev->debugfs_dir
and utilized in subsequent debugfs calls.

Additionally, since accel_dev->debugfs_dir is assured to be non-NULL,
remove the superfluous NULL pointer checks within the adf_dbgfs_add()
and adf_dbgfs_rm().

Fixes: 9260db66 ("crypto: qat - move dbgfs init to separate file")
Signed-off-by: Giovanni Cabiddu <giovanni.cabiddu@intel.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>