staging: rtl8723bs: Remove unnecessary length #define's.

This driver statically defines constants representing the size of
certain structs using literal integers as values.  Replace those
constants with the sizeof() macro.  Other length constants are already
defined in 'linux/ieee80211.h'; remove those #define's.

Signed-off-by: Quytelda Kahja <quytelda@tamalin.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>