Compiling the DT file with W=1, DTC warns like follows:

Warning (unit_address_vs_reg): Node /opp_table0/opp@1000000000 has a
unit name, but no reg property

Fix this by replacing '@' with '-' as the OPP nodes will never have a
"reg" property.
Reported-by: NKrzysztof Kozlowski <krzk@kernel.org>
Reported-by: NMasahiro Yamada <yamada.masahiro@socionext.com>
Suggested-by: NMark Rutland <mark.rutland@arm.com>
Signed-off-by: NViresh Kumar <viresh.kumar@linaro.org>
Acked-by: NRob Herring <robh@kernel.org>
Signed-off-by: NMasahiro Yamada <yamada.masahiro@socionext.com>