Don't require CONFIG_CRC7 to build wl1251/wl12xx for SDIO

CRC7 functions are only used in the SPI code for these drivers, so it's
unnecessary for the SDIO drivers to depend on CONFIG_CRC7. See, for
example, commit a011130265e9 ("wl12xx: remove unused crc7 references")
in Linus's tree.

Change-Id: Idaa5c89e27d6a1190908f949644bcd0f3d1e6a54