staging: rtl8723bs: Fix assignment in if condition in os_dep/sdio_intf.c

ERROR: do not use assignment in if condition
Detected by scripts/checkpatch.pl -f

Signed-off-by: Bingyu Zhou <rain.by.zhou@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>