staging: rtl8723bs: hal: fix spelling mistake "singal" -> "signal"

There are multiple spelling mistakes in variable names, fix these.

Signed-off-by: Colin Ian King <colin.king@canonical.com>
Reviewed-by: Mukesh Ojha <mojha@codeaurora.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>