ARM: dts: dm816x: Correct the state of the write protect pin

Commit 599c376c ("ARM: dts: Fix gpio interrupts for dm816x")
corrected some problems with the MMC.  However, it gets the write
protect pin backwards.  It needs to be ACTIVE_HIGH not ACTIVE_LOW.

Cc: Rob Herring <robh+dt@kernel.org>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Russell King <linux@armlinux.org.uk>
Cc: Tony Lindgren <tony@atomide.com>
Signed-off-by: Mihail Grigorov <michael.grigorov@konsulko.com>
Signed-off-by: Tom Rini <trini@konsulko.com>
Signed-off-by: Tony Lindgren <tony@atomide.com>