Split increments to silence a compiler warning.

Upstream clang complains that this line may be a possible misuse of the
comma operator, since the result from "p++" is being discarded. Rather
than overcomplicate things with a static_cast<void>(), it is easiest to
just move this to a separate statement.

Change-Id: I5d005eb82a02430f691f99a2f1e8b7237320f84a