staging: r8188eu: remove unused function SetBcnCtrlReg()

Remove unused function SetBcnCtrlReg().

Signed-off-by: Michael Straube <straube.linux@gmail.com>
Link: https://lore.kernel.org/r/20210830092153.9283-5-straube.linux@gmail.com


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