ARM: s3c24xx: Correct SD card write protect detection on Mini2440

The mini2440 computer uses "active high" to signal that the "write protect"
of the inserted MMC is set. The current code uses the opposite, leading to
a wrong detection of write protection. The solution is simply to use
".wprotect_invert = 1" in the description of the MMC.

Signed-off-by: Cedric Roux <sed@free.fr>
Signed-off-by: Krzysztof Kozlowski <krzk@kernel.org>