USB: switch maintainership of chipidea to Peter

Alexander isn't able to maintain the Chipidea code anymore, and as Peter
has been acting as the de-facto maintainer anyway, make it official.

Acked-by: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Acked-by: Peter Chen <Peter.Chen@freescale.com>
Acked-by: Marc Kleine-Budde <mkl@pengutronix.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>