MAINTAINERS: drop OMAP USB and MUSB maintainership

Now that I have switched to another company, I won't
be able to help by maintaining OMAP USB Support and/or
the MUSB driver.

OMAP USB Support is left Orphaned. MUSB's new
maintainer will be Bin Liu from Texas Instruments
who has accepted to take over starting with v4.6.

Cc: Bin Liu <b-liu@ti.com>
Acked-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Felipe Balbi <balbi@kernel.org>