platform/chrome: wilco_ec: convert stream-like files from nonseekable_open -> stream_open

Eliminate the following coccicheck warning:
./drivers/platform/chrome/wilco_ec/telemetry.c:259:1-17: WARNING:
telem_fops: .read() and .write() have stream semantic; safe to change
nonseekable_open -> stream_open.

Reported-by: Abaci Robot <abaci@linux.alibaba.com>
Signed-off-by: Yang Li <yang.lee@linux.alibaba.com>
Signed-off-by: Enric Balletbo i Serra <enric.balletbo@collabora.com>
Link: https://lore.kernel.org/r/1612688918-63132-1-git-send-email-yang.lee@linux.alibaba.com