staging/atomisp: remove redundant null check on frame

There is no need to perform a null check on frame as there is an earlier
null check check and return hence making the null check redundant.
Remove it.

Detected by CoverityScan, CID#1416563 ("Logically Dead Code")

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