staging: r8188eu: convert return type of Hal_GetChnlGroup88E() to void

staging: r8188eu: convert return type of Hal_GetChnlGroup88E() to void

After the removal of 5GHz code from Hal_GetChnlGroup88E() the function
always returns true now. Convert the return type to void and change the
only user Hal_ReadTxPowerInfo88E() accordingly.

Acked-by: Phillip Potter <phil@philpotter.co.uk>
Acked-by: Martin Kaiser <martin@kaiser.cx>
Signed-off-by: Michael Straube <straube.linux@gmail.com>
Link: https://lore.kernel.org/r/20210813073109.25609-3-straube.linux@gmail.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>