soundwire: remove useless initializations

No need for explicit initialization of page and ssp fields, they are
already zeroed with a memset.

Detected with cppcheck:

[drivers/soundwire/bus.c:309]: (style) Variable 'msg->page' is
reassigned a value before the old one has been used.

Signed-off-by: Pierre-Louis Bossart <pierre-louis.bossart@linux.intel.com>
Reviewed-by: Takashi Iwai <tiwai@suse.de>
Signed-off-by: Vinod Koul <vkoul@kernel.org>