checkpatch: Check for illegal return codes

The only legal integer return is 0, anything else
following "return" should be -ERRCODE or a function.

http://lkml.org/lkml/2010/7/23/318


  There's lots of "return -1;" statements in this patch - it's obscene
  that this is used to indicate "some error occurred" in kernel space
  rather than a real errno value - even when an existing function
  (eg, request_irq) gave you an error code already.

  Please note this for the future - and please review patches on this
  point internally first.

Change-Id: I16268b2ee034f0b3b899115e45c28acfa734ddec
Signed-off-by: Patrick Pannuto <ppannuto@codeaurora.org>
(cherry picked from commit 39531a47164294315b5a7256b520fe22d6e87013)