mwifiex: Change variable type to bool

The variables cancel_scan_cmd, enable_data, hs_activate and valid are
only assigned the values true and false. Change its type to bool.

The simplified semantic patch that find this problem is as
follows (http://coccinelle.lip6.fr/

):

@exists@
type T;
identifier b;
@@
- T
+ bool
  b = ...;
  ... when any
  b = \(true\|false\)

Signed-off-by: Peter Senna Tschudin <peter.senna@gmail.com>
Acked-by: Bing Zhao <bzhao@marvell.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>