staging: comedi: drivers: remove remaining devpriv macros

The remaining comedi drivers that still have a devpriv macro
are all pretty straight forward for removing the devpriv
macro.

This macro relies on a local variable having a specific name.
Remove its use by replacing it with a local variable where
used.

The inline function alloc_private(), used to kzalloc the
dev->private memory, returns non-zero if there is an error.
Fix all the alloc_private() calls accordingly and remove any
kernel messages or obvious comments that still exist in the
drivers. Leave a comment in the skel driver.

Signed-off-by: H Hartley Sweeten <hsweeten@visionengravers.com>
Cc: Ian Abbott <abbotti@mev.co.uk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>