hw/sd.c: When setting ADDRESS_ERROR bit, don't clear everything else

Fix a typo that meant that ADDRESS_ERRORs setting or clearing write
protection would clear every other bit in the status register.

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Signed-off-by: Andrzej Zaborowski <andrew.zaborowski@intel.com>
