nvidiactl: Return success if no Nvidia card was found

Currently, on systems with no Nvidia card, the script returns 1, which
is considered an error. This causes the systemd service unit running
this script to be shown as failed, and these systems are marked as
*degraded* by systemd (`systemctl`, `systemdctl status`).

But, having a system with no Nvidia card is totally fine, as there are
such systems, and therefore shouldn’t be considered an error.

Only return an error, if there really is some incorrect behavior.

nvidiactl/nvidiactl

@@ -13,7 +13,7 @@ if [ -z ${nvver} ] ; then
     echo >&2 "WARNING: no nvidia card found.."
     rm -f /node/usr_share_mxgfx
     ln -sf /usr/share/mxgfx-generic /node/usr_share_mxgfx
-    exit 1
+    exit 0
 fi
 
 pciids="${PCIIDHINT_DIR}/${kver}-${nvver} ${PCIIDHINT_DIR}/${nvver}"