usb: pci-quirks: Minor cleanup for AMD PLL quirk

usb_amd_find_chipset_info() is used for chipset detection for
several quirks. It is strange that its return value indicates
the need for the PLL quirk, which means it is often ignored.
This patch adds a function specifically for checking the PLL
quirk like the other ones. Additionally, rename probe_result to
something more appropriate.

Signed-off-by: Ryan Kennedy <ryan5544@gmail.com>
Acked-by: Alan Stern <stern@rowland.harvard.edu>
Link: https://lore.kernel.org/r/20190704153529.9429-3-ryan5544@gmail.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>