ehci-mxc: Fix host power mask bit for i.MX25

The correct bit for H1_PM is 16, not 8, which is the DP pull-up impedance
selection bit.

This issue has been reported by Eric Bénard <eric@eukrea.com> and fixed by
Christoph Fritz <chf.fritz@googlemail.com> on Linux, from which these #define-s
had been copied.

Signed-off-by: Benoît Thébaudeau <benoit.thebaudeau@advansee.com>
Cc: Stefano Babic <sbabic@denx.de>
Cc: Marek Vasut <marex@denx.de>