i2c: cadence: allow COMPILE_TEST

[ Upstream commit 0b0dcb3882c8f08bdeafa03adb4487e104d26050 ]

Driver builds fine with COMPILE_TEST. Enable it for wider test coverage
and easier maintenance.

Signed-off-by: Wolfram Sang <wsa@kernel.org>
Acked-by: Michal Simek <michal.simek@xilinx.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>