drivers/staging: delete double assignment

Delete successive assignments to the same location.  In three of the cases,
the two assignments are identical.  In the case of the file
rt2860/common/cmm_aes.c, the assigned variable i is never used, so both
assignments are dropped.

A simplified version of the semantic match that finds this problem is as
follows: (http://coccinelle.lip6.fr/)

// <smpl>
@@
expression i;
@@

*i = ...;
 i = ...;
// </smpl>

Signed-off-by: Julia Lawall <julia@diku.dk>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>