Fix build with clang in C++11 mode

Now that we're in C++11 mode by default, clang complains about switch
statements with case values not matching the type -- since some
binder_driver_return_protocol values are > 0x7fffffff, we need to make
the switch statements operate on uint32_t rather than int32_t.

BUG: 18466763
Change-Id: Iedbfd5c7a3d3d9f087d2eab4ff21343ad7a2a448
Signed-off-by: Bernhard Rosenkränzer <Bernhard.Rosenkranzer@linaro.org>