staging: atomisp: remove redundant check for client being null

The previous statement checks if client is null, so the null check
when assigning dev is redundant and can be removed.

Detected by CoverityScan, CID#1416555 ("Logically Dead Code")

Signed-off-by: Colin Ian King <colin.king@canonical.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>