media: sun6i-csi: clarify return value, fix uninited variable and add missing static

This fixes three smatch warnings:

drivers/media/platform/sunxi/sun6i-csi/sun6i_csi_bridge.c:629:15: warning: 'enabled' may be used uninitialized [-Wmaybe-uninitialized]
drivers/media/platform/sunxi/sun6i-csi/sun6i_csi_bridge.c:439 sun6i_csi_bridge_s_stream() warn: missing error code 'ret'
drivers/media/platform/sunxi/sun6i-csi/sun6i_csi_bridge.c:682 sun6i_csi_bridge_notifier_bound() error: uninitialized symbol 'enabled'.

Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab@kernel.org>