ARM: dts: Set USB bus voting to nominal on sdxprairie

Currently USB driver is voting for 2.5 GBps bandwidth which
is resulting into snoc running at turbo. Hence to run snoc
at nominal, vote for 1.25 GBps bandwidth.

Change-Id: Idc15fc40b0c32d7a60aa061b3c9de9e645e265d9
Signed-off-by: Mayank Rana <mrana@codeaurora.org>