staging: r8188eu: make OFDM_24G_Diff a 1-D array

Make OFDM_24G_Diff one-dimensional array. This driver uses only
OFDM_24G_Diff[0].

Acked-by: Michael Straube <straube.linux@gmail.com>
Signed-off-by: Martin Kaiser <martin@kaiser.cx>
Link: https://lore.kernel.org/r/20220105083426.177128-7-martin@kaiser.cx


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