staging: rtl8192e: Fix conflicting types error with net_device.

staging: rtl8192e: Fix conflicting types error with net_device.

Add a pre-declaration of struct net_device so the compiler is able to
use rtl_pci.h / rtl_cam.h.

Signed-off-by: Teddy Engel <engel.teddy@gmail.com>
Reported-by: kernel test robot <lkp@intel.com>
Closes: https://lore.kernel.org/oe-kbuild-all/202406250858.L8rJMHQm-lkp@intel.com/
Fixes: 7dff0b27d9c8 ("staging: rtl8192e: Remove unnecessary pre-declaration of struct net_device")
Tested-by: Philipp Hortmann <philipp.g.hortmann@gmail.com>
Link: https://lore.kernel.org/r/20240625163334.11117-1-engel.teddy@gmail.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>