IDE: ide-floppy, remove unnecessary NULL check

Stanse found that rq in ide_floppy_callback cannot be NULL, because it
is dereferenced all around. So remove the superfluous check.

This appeared after blk_* macros removal.

Signed-off-by: Jiri Slaby <jslaby@suse.cz>
Signed-off-by: David S. Miller <davem@davemloft.net>