block/swim: Don't log an error message for an invalid ioctl

The 'eject' shell command may send various different ioctl commands.
This leads to error messages on the console even though the FDEJECT
ioctl succeeds.

~# eject floppy
SWIM floppy_ioctl: unknown cmd 21257
SWIM floppy_ioctl: unknown cmd 1

Don't log an error message for an invalid ioctl, just do as the
swim3 driver does and return -ENOTTY.

Cc: Laurent Vivier <lvivier@redhat.com>
Cc: Jens Axboe <axboe@kernel.dk>
Cc: stable@vger.kernel.org # v4.14+
Tested-by: Stan Johnson <userm57@yahoo.com>
Signed-off-by: Finn Thain <fthain@telegraphics.com.au>
Acked-by: Laurent Vivier <lvivier@redhat.com>
Reviewed-by: Geert Uytterhoeven <geert@linux-m68k.org>
Signed-off-by: Jens Axboe <axboe@kernel.dk>