staging: rtl8712: Correct a typo in a comment

Correct a single typo in a comment.
Misspelling found using checkpatch.pl.

Signed-off-by: R Veera Kumar <vkor@vkten.in>
Link: https://lore.kernel.org/r/20200319094358.GA2751@tulip.local


Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>