samples: vfio-mdev: Fix missing pci_disable_device() in mdpy_fb_probe()

Add missing pci_disable_device() in fail path of mdpy_fb_probe().
Besides, fix missing release functions in mdpy_fb_remove().

Fixes: cacade19

 ("sample: vfio mdev display - guest driver")
Signed-off-by: Shang XiaoJing <shangxiaojing@huawei.com>
Link: https://lore.kernel.org/r/20221208013341.3999-1-shangxiaojing@huawei.com
Signed-off-by: Alex Williamson <alex.williamson@redhat.com>