floppy: cleanup: expand the R/W / format command macros

Various macros were used to access raw_cmd for R/W or format commands
without making it obvious that raw_cmd->cmd[] was used. Let's expand
the macros to make this more obvious.

Link: https://lore.kernel.org/r/20200224212352.8640-10-w@1wt.euSigned-off-by: Willy Tarreau <w@1wt.eu>
Signed-off-by: Denis Efremov <efremov@linux.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>