soundwire: cadence: remove useless variable incrementation

Fix cppcheck warning:

drivers/soundwire/cadence_master.c:992:9: style: Variable 'offset' is
assigned a value that is never used. [unreadVariable]
 offset += stream->num_out;
        ^

Signed-off-by: Pierre-Louis Bossart <pierre-louis.bossart@linux.intel.com>
Link: https://lore.kernel.org/r/20200113211025.27973-3-pierre-louis.bossart@linux.intel.com


Signed-off-by: Vinod Koul <vkoul@kernel.org>