soundwire: add argument to function definition

Checkpatch warns that function definition of __sdw_register_driver
misses argument, so add it

WARNING: function definition argument 'struct module *' should also have
an identifier name

Signed-off-by: Vinod Koul <vkoul@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>