staging: comedi: don't expose comedi_get_{read, write}_subdevice

These two inline helper function in comedidev.h are only used in
comedi_fops.c. They return information that should only be used
by the comedi core.

Move both functions to comedi_fops.c so they aren't exposed to
the comedi drivers. Also, remove the inline tag and let the
compiler figure it out.

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>