USB: EHCI: tegra: make use of ehci->priv

Rather than allocating struct tegra_ehci_hcd separately, use struct
ehci_hcd's priv field instead.

Signed-off-by: Stephen Warren <swarren@nvidia.com>
Acked-by: Alan Stern <stern@rowland.harvard.edu>
Tested-by: Thierry Reding <thierry.reding@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>