staging: r8188eu: mark IS_MCAST as bool

Mark IS_MCAST as bool as it returns true/false.

Reviewed-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Vihas Makwana <makvihas@gmail.com>
Link: https://lore.kernel.org/r/20220302204737.49056-15-makvihas@gmail.com


Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>