staging: r8188eu: remove HW_VAR_BCN_VALID from GetHwReg8188EU()

staging: r8188eu: remove HW_VAR_BCN_VALID from GetHwReg8188EU()

The HW_VAR_BCN_VALID from GetHwReg8188EU() just calls rtw_read8().
Remove HW_VAR_BCN_VALID from GetHwReg8188EU() and call rtw_read8()
directly. Move the call to a new function to indicate what it actually
does. This is part of the ongoing effort to get rid of the unwanted
hal layer.

Signed-off-by: Michael Straube <straube.linux@gmail.com>
Link: https://lore.kernel.org/r/20220331130522.6648-3-straube.linux@gmail.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>