firmware: arm_ffa: Fix memory corruption in ffa_msg_send2()

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: 02c19d84c7c5 ("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>