staging: rtl8188eu: change type of is_cck_rate - style

The variable is_cck_rate is used for boolean values, so change the
type from u8 to bool. The initializations to zero and use of ternary
operator in the assignments are unnecessary, remove them as well.

Suggested-by: Joe Perches <joe@perches.com>
Signed-off-by: Michael Straube <straube.linux@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>