ARM: davinci: da830-evm: fix GPIO lookup for OHCI

The fixed regulator driver doesn't specify any con_id for gpio lookup
so it must be NULL in the table entry.

Fixes: 274e4c33

 ("ARM: davinci: da830-evm: add a fixed regulator for ohci-da8xx")
Cc: stable@vger.kernel.org
Signed-off-by: Bartosz Golaszewski <bgolaszewski@baylibre.com>
Signed-off-by: Sekhar Nori <nsekhar@ti.com>