firmware: arm_ffa: Fix memory corruption in ffa_msg_send2()

The "msg" pointer is a struct and msg->offset is the sizeof(*msg).  The
pointer here math means the memcpy() will write outside the bounds.
Cast "msg" to a u8 pointer to fix this.

Fixes: 02c19d8 ("firmware: arm_ffa: Add support for FFA_MSG_SEND2")
Signed-off-by: Dan Carpenter <dan.carpenter@linaro.org>
Link: https://lore.kernel.org/r/cd5fb6b5-81fa-4a6d-b2b8-284ca704bbff@moroto.mountain
Signed-off-by: Sudeep Holla <sudeep.holla@arm.com>

drivers/firmware/arm_ffa/driver.c

@@ -363,7 +363,7 @@ static int ffa_msg_send2(u16 src_id, u16 dst_id, void *buf, size_t sz)
 	msg->offset = sizeof(*msg);
 	msg->send_recv_id = src_dst_ids;
 	msg->size = sz;
-	memcpy(msg + msg->offset, buf, sz);
+	memcpy((u8 *)msg + msg->offset, buf, sz);
 
 	/* flags = 0, sender VMID = 0 works for both physical/virtual NS */
 	invoke_ffa_fn((ffa_value_t){