scsi: ibmvscsi: Remove unnecessary cast

Fix the following coccicheck warning:
WARNING: casting value returned by memory allocation function is useless.

Link: https://lore.kernel.org/r/1615515534-1250-1-git-send-email-wangqing@vivo.comSigned-off-by: Wang Qing <wangqing@vivo.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>

drivers/scsi/ibmvscsi/ibmvscsi.c

@@ -717,8 +717,7 @@ static int map_sg_data(struct scsi_cmnd *cmd,
 
 	/* get indirect table */
 	if (!evt_struct->ext_list) {
-		evt_struct->ext_list = (struct srp_direct_buf *)
-			dma_alloc_coherent(dev,
+		evt_struct->ext_list = dma_alloc_coherent(dev,
 					   SG_ALL * sizeof(struct srp_direct_buf),
 					   &evt_struct->ext_list_token, 0);
 		if (!evt_struct->ext_list) {