rtlwifi: Fix spelling of 'download'

downlaod -> download

Signed-off-by: Ding Senjie <dingsenjie@yulong.com>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>
Link: https://lore.kernel.org/r/20210521062734.21284-1-dingsenjie@163.com