staging: wfx: correctly cast data on big-endian targets

When built for a big-endian target, original code caused error:

    include/uapi/linux/swab.h:242:29: note: expected '__u32 * {aka unsigned int *}' but argument is of type 'struct hif_mib_protected_mgmt_policy *'

Fixes: f95a29d4 ("staging: wfx: add HIF commands helpers")
Reported-by: kbuild test robot <lkp@intel.com>
Reported-by: Stephen Rothwell <sfr@canb.auug.org.au>
Signed-off-by: Jérôme Pouiller <jerome.pouiller@silabs.com>
Link: https://lore.kernel.org/r/20191008094232.10014-5-Jerome.Pouiller@silabs.comSigned-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/staging/wfx/hif_tx_mib.h

@@ -145,7 +145,7 @@ static inline int hif_set_mfp(struct wfx_vif *wvif, bool capable, bool required)
 	}
 	if (!required)
 		val.unpmf_allowed = 1;
-	cpu_to_le32s(&val);
+	cpu_to_le32s((uint32_t *) &val);
 	return hif_write_mib(wvif->wdev, wvif->id,
 			     HIF_MIB_ID_PROTECTED_MGMT_POLICY,
 			     &val, sizeof(val));