soundwire: add a blank line between functions

For improving code readability it helps to have a blank line between
function so add when missing.

Checkpatch complains:
CHECK: Please use a blank line after function/struct/union/enum
declarations

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