usb: typec: fix potential array underflow in ucsi_ccg_sync_control()

commit e56aac6e upstream.

The "command" variable can be controlled by the user via debugfs.  The
worry is that if con_index is zero then "&uc->ucsi->connector[con_index
- 1]" would be an array underflow.

Fixes: 170a6726 ("usb: typec: ucsi: add support for separate DP altmode devices")
Signed-off-by: Dan Carpenter <dan.carpenter@linaro.org>
Reviewed-by: Heikki Krogerus <heikki.krogerus@linux.intel.com>
Link: https://lore.kernel.org/r/c69ef0b3-61b0-4dde-98dd-97b97f81d912@stanley.mountain


Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
[Minor context change fixed.
 13f2ec31 ("usb: typec: ucsi: simplify command sending API") rename
 ucsi_ccg_sync_write to ucsi_ccg_sync_control in v6.11, so this patch is
 applied in ucsi_ccg_sync_write in v6.6.]
Signed-off-by: Bin Lan <bin.lan.cn@windriver.com>
Signed-off-by: He Zhe <zhe.he@windriver.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>