of: Add vendor prefix for ROHM Semiconductor

ROHM Semiconductor Co., Ltd. offer PMICs, touchscreen controllers etc.
http://www.rohm.com/web/global/

Signed-off-by: Marek Vasut <marek.vasut+renesas@gmail.com>
Cc: Rob Herring <robh@kernel.org>
Cc: Geert Uytterhoeven <geert+renesas@glider.be>
Acked-by: Geert Uytterhoeven <geert+renesas@glider.be>
Signed-off-by: Rob Herring <robh@kernel.org>