floppy: cleanup: make perpendicular_mode() not rely on current_fdc anymore

Now the fdc is passed in argument so that the function does not
use current_fdc anymore.

It's worth noting that there's still a single raw_cmd pointer
specific to the current fdc. It may make sense to have one per
fdc in the future. In addition, cont->done() still relies on the
current drive and current raw_cmd.

Link: https://lore.kernel.org/r/20200331094054.24441-17-w@1wt.eu


Signed-off-by: Willy Tarreau <w@1wt.eu>
Signed-off-by: Denis Efremov <efremov@linux.com>