pc: Fix floppy drives with if=none

Commit 63ffb564 broke floppy devices specified on the command line like
-drive file=...,if=none,id=floppy -global isa-fdc.driveA=floppy because it
relies on drive_get() which works only with -fda/-drive if=floppy.

This patch resembles what we're already doing for IDE, i.e. remember the floppy
device that was created and use that to extract the BlockDriverStates where
needed.

Signed-off-by: Kevin Wolf <kwolf@redhat.com>
Reviewed-by: Markus Armbruster <armbru@redhat.com>
diff --git a/hw/pc.h b/hw/pc.h
index b8ad9a3..4515006 100644
--- a/hw/pc.h
+++ b/hw/pc.h
@@ -142,11 +142,12 @@
 void pc_vga_init(PCIBus *pci_bus);
 void pc_basic_device_init(qemu_irq *gsi,
                           ISADevice **rtc_state,
+                          ISADevice **floppy,
                           bool no_vmport);
 void pc_init_ne2k_isa(NICInfo *nd);
 void pc_cmos_init(ram_addr_t ram_size, ram_addr_t above_4g_mem_size,
                   const char *boot_device,
-                  BusState *ide0, BusState *ide1,
+                  ISADevice *floppy, BusState *ide0, BusState *ide1,
                   ISADevice *s);
 void pc_pci_device_init(PCIBus *pci_bus);