Testing for the write protection bit to determine if a card is write
protected or not is wrong. The bit may have the wrong value for
permanently plugged cards (eMMC) or for boards using a GPIO for
write protection detection.
Since the core will test for write protection before actually
calling into the driver this test can just be removed.

Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>