hw/pc.c: Fix use-while-uninitialized of fd_type[]

Fix a use-while-uninitialized of the fd_type[] array (introduced
in commit 34d4260e1, noticed by Coverity). This is more theoretical
than practical, since it's quite hard to get here with floppy==NULL
(the qdev_try_create() of the isa-fdc device has to fail).

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>
