HID: intel_ish-hid: Move header size check to inside the loop

With the headersize check outside of the loop, the second time through
the loop the: "payload_len = recv_msg->hdr.size;" statement may deref
recv_msg while it is pointing outside of our input buffer.

Move the headersize check to inside the loop to fix this.

Signed-off-by: Hans de Goede <hdegoede@redhat.com>
Reviewed-by: Benjamin Tissoires <benjamin.tissoires@redhat.com>
Acked-by: Srinivas Pandruvada <srinivas.pandruvada@linux.intel.com>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>