sunrpc: removed redundant procp check

since vs_proc pointer is dereferenced before getting it's address there's
no need to check for NULL.

Found by Linux Verification Center (linuxtesting.org) with SVACE.

Fixes: 8e5b6773

 ("SUNRPC: Add a callback to initialise server requests")
Signed-off-by: Aleksandr Aprelkov <aaprelkov@usergate.com>
Reviewed-by: Jeff Layton <jlayton@kernel.org>
Signed-off-by: Chuck Lever <chuck.lever@oracle.com>