firmware_loader: revert removal of the fw_fallback_config export

Christoph's patch removed two unsused exported symbols, however, one
symbol is used by the firmware_loader itself.  If CONFIG_FW_LOADER=m so
the firmware_loader is modular but CONFIG_FW_LOADER_USER_HELPER=y we fail
the build at mostpost.

ERROR: modpost: "fw_fallback_config" [drivers/base/firmware_loader/firmware_class.ko] undefined!

This happens because the variable fw_fallback_config is built into the
kernel if CONFIG_FW_LOADER_USER_HELPER=y always, so we need to grant
access to the firmware loader module by exporting it.

Revert only one hunk from his patch.

Fixes: 73960473

 ("firmware_loader: remove unused exports")
Reported-by: Randy Dunlap <rdunlap@infradead.org>
Signed-off-by: Luis Chamberlain <mcgrof@kernel.org>
Link: https://lore.kernel.org/r/20200424184916.22843-1-mcgrof@kernel.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>