ARM: dts: imx53: Fix 'usbphy@x' node with unit name and no reg property

The following build warnings are seen with W=1:

Warning (unit_address_vs_reg): Node /soc/aips@50000000/usbphy@0 has a unit name, but no reg property
Warning (unit_address_vs_reg): Node /soc/aips@50000000/usbphy@1 has a unit name, but no reg property

Fix these warnings by changing '@' to '-'.

Signed-off-by: Marco Franchi <marco.franchi@nxp.com>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>