wl12xx: fix sdio_test kconfig/build errors

The wl12xx sdio_test code uses wl12xx_get_platform_data, which is
only present when WL12*_SDIO is enabled, so make WL12XX_SDIO_TEST
depend on WL12XX_SDIO so that the needed interface will be present.

sdio_test.c:(.devinit.text+0x13178): undefined reference to `wl12xx_get_platform_data'

Signed-off-by: Randy Dunlap <randy.dunlap@oracle.com>
Cc: Luciano Coelho <luciano.coelho@nokia.com>
Cc: Roger Quadros <roger.quadros@nokia.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>