scsi: ufs: core: sysfs: Prevent div by zero

Prevent a division by 0 when monitoring is not enabled.

Fixes: 1d8613a2 ("scsi: ufs: core: Introduce HBA performance monitor sysfs nodes")
Cc: stable@vger.kernel.org
Signed-off-by: Gwendal Grignou <gwendal@chromium.org>
Link: https://lore.kernel.org/r/20241120062522.917157-1-gwendal@chromium.org


Reviewed-by: Can Guo <quic_cang@quicinc.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>