NFS: remove unneeded check in decode_devicenotify_args()

NFS: remove unneeded check in decode_devicenotify_args()

This is an automated ID intended to aid in discovery of potential security vulnerabilities. The actual impact and attack plausibility have not yet been proven.
This ID is fixed in Linux Kernel version v5.4.189 by commit efc605469e4773690bfd09aee946ebd62bde7609, it was introduced in version v4.0 by commit a4f743a6bb201662962fa888e3f978583d61691e. For more details please see the references link.