wil6210: check len before memcpy() calls

memcpy() in wmi_set_ie() and wmi_update_ft_ies() is called with
src == NULL and len == 0. This is an undefined behavior. Fix it
by checking "ie_len > 0" before the memcpy() calls.

As suggested by GCC documentation:
"The pointers passed to memmove (and similar functions in <string.h>)
must be non-null even when nbytes==0, so GCC can use that information
to remove the check after the memmove call." [1]

[1] https://gcc.gnu.org/gcc-4.9/porting_to.html

Cc: Maya Erez <merez@codeaurora.org>
Cc: Kalle Valo <kvalo@codeaurora.org>
Cc: "David S. Miller" <davem@davemloft.net>
Cc: stable@vger.kernel.org
Signed-off-by: Denis Efremov <efremov@linux.com>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>

drivers/net/wireless/ath/wil6210/wmi.c

@@ -2505,6 +2505,7 @@ int wmi_set_ie(struct wil6210_vif *vif, u8 type, u16 ie_len, const void *ie)
 	cmd->mgmt_frm_type = type;
 	/* BUG: FW API define ieLen as u8. Will fix FW */
 	cmd->ie_len = cpu_to_le16(ie_len);
+	if (ie_len)
 		memcpy(cmd->ie_info, ie, ie_len);
 	rc = wmi_send(wil, WMI_SET_APPIE_CMDID, vif->mid, cmd, len);
 	kfree(cmd);
@@ -2541,6 +2542,7 @@ int wmi_update_ft_ies(struct wil6210_vif *vif, u16 ie_len, const void *ie)
 	}
 
 	cmd->ie_len = cpu_to_le16(ie_len);
+	if (ie_len)
 		memcpy(cmd->ie_info, ie, ie_len);
 	rc = wmi_send(wil, WMI_UPDATE_FT_IES_CMDID, vif->mid, cmd, len);
 	kfree(cmd);