ehci: update driver with another generic change

Update the OMAP EHCI driver in accordance with below patch
introduced in generic EHCI driver.

commit 914b701280a76f96890ad63eb0fa99bf204b961c
USB: EHCI: use the new clear_tt_buffer interface

Without this EHCI becomes unusable when a compound device
DELL USB keyboard)is connected and disconnected.

Signed-off-by: Ajay Kumar Gupta <ajay.gupta@ti.com>
Signed-off-by: Tony Lindgren <tony@atomide.com>