staging: r8188eu: remove HW_VAR_BCN_VALID from SetHwReg8188EU()

staging: r8188eu: remove HW_VAR_BCN_VALID from SetHwReg8188EU()

The HW_VAR_BCN_VALID case in SetHwReg8188EU() just calls rtw_write8().
Remove HW_VAR_BCN_VALID from SetHwReg8188EU() and call rtw_write8()
directly. Move the call to a new function to indicate what it actually
does. This is part of the ongoing effort to getrid of the unwanted hal
layer.

Signed-off-by: Michael Straube <straube.linux@gmail.com>
Link: https://lore.kernel.org/r/20220329202141.7028-9-straube.linux@gmail.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>