staging: wfx: avoid compiler warning on empty array

When CONFIG_OF is disabled, gcc-9 produces a warning about the
wfx_sdio_of_match[] array having a declaration without a dimension:

drivers/staging/wfx/bus_sdio.c:159:34: error: array 'wfx_sdio_of_match' assumed to have one element [-Werror]
  159 | static const struct of_device_id wfx_sdio_of_match[];
      |                                  ^~~~~~~~~~~~~~~~~

Move the proper declaration up and out of the #ifdef instead.

Fixes: a7a91ca5 ("staging: wfx: add infrastructure for new driver")
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Cc: Jerome Pouiller <Jerome.Pouiller@silabs.com>
Link: https://lore.kernel.org/r/20200429142119.1735196-1-arnd@arndb.de


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