net: Fix typo in ipw2x00/libipw_rx.c

Correct spelling in "suppported" to "supported" in
drivers/net/wireless/ipw2x00/libipw_rx.c

Signed-off-by: Masanari Iida <standby24x7@gmail.com>
Reviewed-by: Jesper Juhl <jj@chaosbits.net>
Signed-off-by: John W. Linville <linville@tuxdriver.com>