staging: bcm: add 32-bit host dependency

The driver uses a 32-bit variable to store a pointer, causing a couple of
warnings:

../drivers/staging/bcm/CmHost.c: In function 'StoreCmControlResponseMessage':
../drivers/staging/bcm/CmHost.c:1503:3: error: cast to pointer from integer of different size [-Werror=int-to-pointer-cast]
   (struct bcm_connect_mgr_params *) ntohl(
   ^
../drivers/staging/bcm/CmHost.c:1546:3: error: cast to pointer from integer of different size [-Werror=int-to-pointer-cast]
   (struct bcm_connect_mgr_params *) ntohl(
   ^
../drivers/staging/bcm/CmHost.c:1564:3: error: cast to pointer from integer of different size [-Werror=int-to-pointer-cast]
   (struct bcm_connect_mgr_params *) ntohl(

I fixed other warnings in an earlier commit 9f1c75ac ("staging/bcm: fix most
build warnings"), but couldn't figure out what was the intended behavior on
64-bit machines here.

The driver was removed in linux-3.19, commit d09e9b16 ("staging: bcm: remove
driver") which explains that it never worked on 64-bit machines. This adds
a Kconfig dependency instead to prevent it from being built in the known
broken configuration. This workaround applies to v2.6.37 or higher.

Fixes: f8942e07 ("staging: Beeceem USB Wimax driver")
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/staging/bcm/Kconfig

 config BCM_WIMAX
        tristate "Beceem BCS200/BCS220-3 and BCSM250 wimax support"
        depends on USB && NET
+	depends on !64BIT
        help
          This is an experimental driver for the Beceem WIMAX chipset used
 	 by Sprint 4G.