PCI: rockchip: Correct the use of FTS mask

We're trying to mask out bits[23:8] while retaining [32:24, 7:0], but we're
doing the inverse.  That doesn't have too much effect, since we're setting
all the [23:8] bits to 1, and the other bits are only relevant for modes
we're currently not using.  But we should get this right.

Fixes: ca198908 ("PCI: rockchip: Fix wrong transmitted FTS count")
Signed-off-by: Brian Norris <briannorris@chromium.org>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Acked-by: Shawn Lin <shawn.lin@rock-chips.com>