scsi: arcmsr: Fix reading empty buffer length

Fix empty buffer length error which causes ARECA CLI app command timeout.

Signed-off-by: ching Huang <ching2048@areca.com.tw>
Link: https://lore.kernel.org/r/4aec4385abc6eab10b575c28130ec615a144492d.camel@areca.com.tw
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>

Author: ching Huang

drivers/scsi/arcmsr/arcmsr_hba.c

@@ -2255,8 +2255,11 @@ static void arcmsr_iop2drv_data_wrote_handle(struct AdapterControlBlock *acb)
 
 	spin_lock_irqsave(&acb->rqbuffer_lock, flags);
 	prbuffer = arcmsr_get_iop_rqbuffer(acb);
-	buf_empty_len = (acb->rqbuf_putIndex - acb->rqbuf_getIndex - 1) &
-		(ARCMSR_MAX_QBUFFER - 1);
+	if (acb->rqbuf_putIndex >= acb->rqbuf_getIndex) {
+		buf_empty_len = (ARCMSR_MAX_QBUFFER - 1) -
+		(acb->rqbuf_putIndex - acb->rqbuf_getIndex);
+	} else
+		buf_empty_len = acb->rqbuf_getIndex - acb->rqbuf_putIndex - 1;
 	if (buf_empty_len >= readl(&prbuffer->data_len)) {
 		if (arcmsr_Read_iop_rqbuffer_data(acb, prbuffer) == 0)
 			acb->acb_flags |= ACB_F_IOPDATA_OVERFLOW;