haven: hh_rm_iface: Avoid integer overflow for req_payload_size calculation

There is a possibility for the calculation to overflow when size is large
enough to overflow when added to the size of payload. Ensure that this
overflow is caught early.

Change-Id: I876fbaa704ba51dc4a9e4eb4d3f7f0eaa749e06d
Signed-off-by: Prakruthi Deepak Heragu <pheragu@codeaurora.org>
Signed-off-by: Swetha Chikkaboraiah <schikk@codeaurora.org>