staging: rtl8188eu: for loop instead of while loop used

The range of elements to fill with zeros is determined by using a roundup macro

Signed-off-by: Ivan Safonov <insafonov@gmail.com>
Reviewed-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>