rndis_wlan: use ARRAY_SIZE instead of sizeof when adding 11g rates

While figuring out the TKIP problem I found a bug in the code which adds the 11g
rates. It's using sizeof instead of ARRAY_SIZE to terminate the for loop. This makes
it fall off the end of the rates array start into the frequency array instead. Running
"iwlist rate" should show the problem as there will always be 32 rates with the last
few being bogus.

The following patch will fix it.

Signed-off-by: Scott Ashcroft <scott.ashcroft@talk21.com>
Signed-off-by: Jussi Kivilinna <jussi.kivilinna@mbnet.fi>
Signed-off-by: John W. Linville <linville@tuxdriver.com>