staging: vc04_services: fix NULL pointer dereference on pointer 'service'

Currently, if pservice is null then service is set to NULL and immediately
afterwards service is dereferenced causing a null pointer dereference. Fix
this by bailing out early of the function with a null return.

Detected by CoverityScan, CID#1419681 ("Explicit null dereferenced")

Signed-off-by: Colin Ian King <colin.king@canonical.com>
Acked-by: Stefan Wahren <stefan.wahren@i2se.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>