media: staging: rkisp1: stats: use consistent bus_info string

Stats entity is using a slightly different bus_info string
"platform: rkisp1" (with a space) instead of "platform:rkisp1" used by
the rest of rkisp1 code.
This causes errors when using v4l2-util tools that uses the bus_info
string to identify the device.

Fixes: 9a28dbd6 ("media: staging: rkisp1: add capture device for statistics")
Signed-off-by: Helen Koike <helen.koike@collabora.com>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>