i40e: Fix an NULL vs IS_ERR() bug for debugfs_create_dir()

stable inclusion
from stable-v5.10.190
commit 8a6cc852f6589d7d6651fb9f7b708c3b3d84e49d
category: bugfix
bugzilla: https://gitee.com/openeuler/kernel/issues/I928UI

Reference: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=8a6cc852f6589d7d6651fb9f7b708c3b3d84e49d



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[ Upstream commit 043b1f18 ]

The debugfs_create_dir() function returns error pointers.
It never returns NULL. Most incorrect error checks were fixed,
but the one in i40e_dbg_init() was forgotten.

Fix the remaining error check.

Fixes: 02e9c290 ("i40e: debugfs interface")
Signed-off-by: Wang Ming <machel@vivo.com>
Tested-by: Pucha Himasekhar Reddy <himasekharx.reddy.pucha@intel.com> (A Contingent worker at Intel)
Signed-off-by: Tony Nguyen <anthony.l.nguyen@intel.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>
Signed-off-by: sanglipeng <sanglipeng1@jd.com>