Staging: rtl8712: Eliminate use of _set_timer

This patch introduces the use of API function mod_timer
instead of driver specific function _set_timer as it is
a more efficient and standard way to update the expire
field of an active timer. Also, definition of function
_set_timer is removed as it is no longer needed after
this change.

Here, these cases are handled using Coccinelle and
semantic patch used for this is as follows:

@@ expression x; expression y;@@

- _set_timer (&x, y);
+ mod_timer (&x, jiffies + msecs_to_jiffies (y));

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