staging: r8188eu: Fix misspelling in comment

As format check raised by scripts/checkpatch.pl, comment in the rtw_ap.c
looks misspelled by accident. Help fix it.

The original error is as below shows:

CHECK: 'followign' may be misspelled - perhaps 'following'?
+Set to 0 (HT pure) under the followign conditions

Signed-off-by: Siou-Jhih, Guo <hallblazzar@gmail.com>
Link: https://lore.kernel.org/r/20211011214803.GA239300@hallblazzar-Precision-5510


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