ide: fix generic_ide_suspend/resume Oops

This patch fixes a regresion introduced by commit 0998d063 (device-core: Ensure
drvdata = NULL when no driver is bound).

Suspend oopses in generic_ide_suspend() because dev_get_drvdata()
returns NULL (dev->p->driver_data == NULL) and this function is not
prepared for this.

Fix is based on Alan Stern's suggestion.

Signed-off-by: Miklos Szeredi <mszeredi@suse.cz>
Acked-by: Rafael J. Wysocki <rjw@sisk.pl>
Signed-off-by: David S. Miller <davem@davemloft.net>