Staging: dgnc: Use goto for error handling

This patch introduces goto statments for error handling
and in cases where a lock needs to be released.

A simplified version of the semantic patch that finds this problem is as
follows: (http://coccinelle.lip6.fr

)

@candidates exists@
identifier f, label;
statement s;
position p1, p2, p3;
@@

  f@p1(...) {
  ...when any

    if@p2(...) {
    ...when any
      s

      return@p3 ...;
    }
  ...when any
  }

@good1 exists@
identifier candidates.f, candidates.label;
statement candidates.s;
position candidates.p1, candidates.p2;
@@

  f@p1(...) {
  ...when any

    if(...) {
    ...when any
      s
      return ...;
    }
    ...when any

    if@p2(...) {...}
  ...when any
 }

@depends on good1@
identifier candidates.f, candidates.label;
position candidates.p1, candidates.p3;
@@

   f@p1(...) {
   ...when any
*  return@p3 ...;
  }

Signed-off-by: Quentin Lambert <lambert.quentin@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>