firmware: arm_scpi: drop unnecessary type cast to scpi_shared_mem

This patch drops the only present type cast of the SCPI payload pointer
to scpi_shared_mem inorder to align with other occurrences, IOW for
consistency.
Tested-by: NKevin Hilman <khilman@baylibre.com>
Reviewed-by: NHeiner Kallweit <hkallweit1@gmail.com>
Signed-off-by: NSudeep Holla <sudeep.holla@arm.com>

drivers/firmware/arm_scpi.c

@@ -453,7 +453,7 @@ static void scpi_tx_prepare(struct mbox_client *c, void *msg)
 	unsigned long flags;
 	struct scpi_xfer *t = msg;
 	struct scpi_chan *ch = container_of(c, struct scpi_chan, cl);
-	struct scpi_shared_mem *mem = (struct scpi_shared_mem *)ch->tx_payload;
+	struct scpi_shared_mem *mem = ch->tx_payload;
 
 	if (t->tx_buf) {
 		if (scpi_info->is_legacy)