staging: comedi: separate out comedi_buf_* functions

Create a new file, comedi_buf.c, to hold all the comedi_async buffer
functions. Currently they are all in drivers.c and really don't have
any association with that source file.
Signed-off-by: H Hartley Sweeten <hsweeten@visionengravers.com>
Signed-off-by: Ian Abbott <abbotti@mev.co.uk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/staging/comedi/Makefile

-comedi-y			:= comedi_fops.o range.o drivers.o
+comedi-y			:= comedi_fops.o range.o drivers.o \
+				   comedi_buf.o
 comedi-$(CONFIG_PROC_FS)	+= proc.o
 comedi-$(CONFIG_COMPAT)		+= comedi_compat32.o