ARM: dts: nxp/imx6sll: fix wrong property name in usbphy node

Property name "phy-3p0-supply" is used instead of "phy-reg_3p0-supply".

Fixes: 9f30b6b1 ("ARM: dts: imx: Add basic dtsi file for imx6sll")
cc: <stable@vger.kernel.org>
Signed-off-by: Xu Yang <xu.yang_2@nxp.com>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>