ARM: davinci: board-da850-evm: fix WP pin polarity for MMC/SD

When booting from MMC/SD in rw mode on DA850 EVM, the system
crashes because the write protect pin should be active high
and not active low. This patch fixes the polarity of the WP pin.

Fixes: bdf0e836 ("ARM: davinci: da850-evm: use gpio descriptor for mmc pins")
Signed-off-by: Adam Ford <aford173@gmail.com>
Signed-off-by: Sekhar Nori <nsekhar@ti.com>