soundwire: Remove startup from swr_driver structure

Remove the startup function declaration from struct
swr_driver as it has been removed as part of
moving soundwire device functionality from swrm
master probe to the swr device probe.

CRs-fixed: 2050710
Change-Id: I2c0a38c609f87c432e3cd29694caf1d2f1a272e2
Signed-off-by: Karthikeyan Mani <kmani@codeaurora.org>