SUNRPC: Clean up use of curly braces in switch cases

Clean up.  Preferred style is not to use curly braces around
switch cases.  I'm about to add another case that needs a third
type cast.

Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
Signed-off-by: Trond Myklebust <Trond.Myklebust@netapp.com>