firmware: arm_ffa: Fix the missing entry in struct ffa_indirect_msg_hdr

As per the spec, one 32 bit reserved entry is missing here, add it.

Signed-off-by: Viresh Kumar <viresh.kumar@linaro.org>
Fixes: 910cc1ac ("firmware: arm_ffa: Add support for passing UUID in FFA_MSG_SEND2")
Reviewed-by: Bertrand Marquis <bertrand.marquis@arm.com>
Message-Id: <28a624fbf416975de4fbe08cfbf7c2db89cb630e.1748948911.git.viresh.kumar@linaro.org>
Signed-off-by: Sudeep Holla <sudeep.holla@arm.com>