scsi: lpfc: Fix the NULL vs IS_ERR() bug for debugfs_create_file()

Since debugfs_create_file() returns ERR_PTR and never NULL, use IS_ERR() to
check the return value.

Fixes: 2fcbc569 ("scsi: lpfc: Make debugfs ktime stats generic for NVME and SCSI")
Fixes: 4c47efc1 ("scsi: lpfc: Move SCSI and NVME Stats to hardware queue structures")
Fixes: 6a828b0f ("scsi: lpfc: Support non-uniform allocation of MSIX vectors to hardware queues")
Fixes: 95bfc6d8 ("scsi: lpfc: Make FW logging dynamically configurable")
Fixes: 9f778708 ("scsi: lpfc: Add debugfs support for cm framework buffers")
Fixes: c490850a

 ("scsi: lpfc: Adapt partitioned XRI lists to efficient sharing")
Signed-off-by: Jinjie Ruan <ruanjinjie@huawei.com>
Link: https://lore.kernel.org/r/20230906030809.2847970-1-ruanjinjie@huawei.com
Reviewed-by: Justin Tee <justin.tee@broadcom.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>