CRAS: use enum type so C++ unittests compile.
CRAS: use enum type so C++ unittests compile.

g++ will wine when converting from unsigned to an enum.

BUG=none
TEST=build and run CRAS on lumpy. Run unittests.

Change-Id: I321605412b1652b394bb1c0bdab080496a0565d9
Signed-off-by: Dylan Reid <c791bfe44996c1eed9c7149a0c5f12a86d58eb85@chromium.org>

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