fix(el3-spmc): use uint64_t for 64-bit type

Using uint64_t is cleaner, even though size_t is 64 bits on all
platforms el3-spmc supports.

Change-Id: I457deb0b7f3df0749cb5368cceda1bb530d039de
Signed-off-by: Demi Marie Obenour <demiobenour@gmail.com>
1 file changed