ARM: dts: i.MX53: fix apparent bug in VPU clks

The VPU on i.MX53 has two distinct clocks for register access and
internal function.

Signed-off-by: Lothar Waßmann <LW@KARO-electronics.de>
Fixes: fbf970f6

 ("ARM: dts: mx53qsb: Enable VPU support")
Cc: <stable@vger.kernel.org>
Signed-off-by: Shawn Guo <shawn.guo@freescale.com>