Both floppy_grab_irq_and_dma() and floppy_release_irq_and_dma() used to
iterate on the global variable while setting up or freeing resources.
Now that they exclusively rely on functions which take the fdc as an
argument, so let's not touch the global one anymore.

Link: https://lore.kernel.org/r/20200331094054.24441-23-w@1wt.euSigned-off-by: Willy Tarreau <w@1wt.eu>
Signed-off-by: Denis Efremov <efremov@linux.com>