scsi: qla2xxx: Remove increment of interface err cnt

Residual underrun is not an interface error, hence no need to increment
that count.

Fixes: dbf1f53c ("scsi: qla2xxx: Implementation to get and manage host, target stats and initiator port")
Cc: stable@vger.kernel.org
Signed-off-by: Saurav Kashyap <skashyap@marvell.com>
Signed-off-by: Nilesh Javali <njavali@marvell.com>
Reviewed-by: Himanshu Madhani <himanshu.madhani@oracle.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>