fix(mhuv2): provide only the usable size of memory

The function mhu_get_max_message_size() for MHUv2 should return only the
available memory for use after considering all the overheads for its own
use.

Signed-off-by: Sathyam Panda <sathyam.panda@arm.com>
Signed-off-by: Vijayenthiran Subramaniam <vijayenthiran.subramaniam@arm.com>
Change-Id: I14ad16e8f4b781e396bca6173077513db74157d5
1 file changed