staging: comedi: Fix reversed test in comedi_device_attach()

Commit 3902a370 (staging: comedi:
refactor comedi_device_attach() a bit) by yours truly introduced an
inverted logic bug in comedi_device_attach() for the case where the
driver expects the device to be configured by driver name rather than
board name.  The result of a strcmp() is being tested incorrectly.  Fix
it.

Thanks to Stephen N Chivers for discovering the bug and suggesting the
fix.

Cc: <stable@vger.kernel.org> # 3.5.x
Signed-off-by: Ian Abbott <abbotti@mev.co.uk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>