staging: rtl8188eu: remove useless variable rtw_AcceptAddbaReq

rtw_AcceptAddbaReq is a static variable, it is set once and never
modified. It is referenced only once, to assign its value to a member
of struct registry_priv with practically the same name.

Get rid of the variable, and move the meaningful part of the comment
near the declaration of the relevant field of struct registry_priv.

Raises a new checkpatch issue, which is fixed in a later commit:
  CHECK: Avoid CamelCase: <bAcceptAddbaReq>

Signed-off-by: Luca Ceresoli <luca@lucaceresoli.net>
Cc: Larry Finger <Larry.Finger@lwfinger.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>