Staging: rtl8712: Eliminate use of _cancel_timer

Use timer API function del_timer_sync instead of driver
specific function _cancel_timer as besides deactivating
a timer, it also ensures that the timer is stopped on all
CPUs before the driver exists. Also, variables
timer_cancelled and bool are removed as they are no longer
needed.

@a@
expression x;
identifier y;
@@

- _cancel_timer (&x, &y);
+ del_timer_sync (&x);

@@type T; identifier a.y;@@

- T y;
...when != y

Signed-off-by: Vaishali Thakkar <vthakkar1994@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>