staging: xgifb: Remove unused variable and if statement

Setting the variable 'refresh_rate = 60;' has no use to the rest of the
function. Hence the if statement setting it and the variable itself can be
removed. This was detected using the following Coccinelle semantic patch:

@@
type T;
identifier i;
constant C;
@@
(
extern T i;
|
- T i;
  <+... when != i
- i = C;
  ...+>
)

Signed-off-by: Rehas Sachdeva <aquannie@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>