staging: rtl8712: Remove space after a cast.

This patch fixes the following checkpatch issue:

CHECK: No space is necessary after a cast

Signed-off-by: Varsha Rao <rvarsha016@gmail.com>
Acked-by: Julia Lawall <julia.lawall@lip6.fr>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>