Staging: dt3155: use the fbuffer pointer instead of looking it up

Instead of passing the minor number and having to look up the fbuffer, just
pass the fbuffer directly to the buffer management code.

Also, to make the code more consistent, change the push_empty() call so
that the fbuffer is passed as the first parameter.

Prototype the printques routine to avoid having to declare it as extern.

Cleanup some of the comments in dt3155_isr.h.

Signed-off-by: H Hartley Sweeten <hsweeten@visionengravers.com>
Cc: Scott Smedley <ss@aao.gov.au>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>