drm/hisilicon: Use pcim_enable_device()

Using the managed function simplifies the error handling. After
unloading the driver, the PCI device should now get disabled as
well.

Signed-off-by: Tian Tao <tiantao6@hisilicon.com>
Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Link: https://patchwork.freedesktop.org/patch/msgid/1608511522-3100-1-git-send-email-tiantao6@hisilicon.com