staging: rtl8192u: Removed assignments from if statements.

Removes assignments from if statements and simplifies unnecessary
0/NULL-checking. The following coccinelle script found the match:
@@
expression E0, E1, E2;
statement S0;
@@
- if (E0 == (E1 = E2))
+ E1 = E2;
+ if (E1 == E0)
S0

Signed-off-by: Chi Pham <fempsci@gmail.com>
Acked-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Signed-off-by: Peter P Waskiewicz Jr <peter.p.waskiewicz.jr@intel.com>