uwb: i1480/GUWA100U: fix firmware download issues

IOGear firmware versions >= 1.4.12224 fail to be downloaded because of a
spurious (and harmless) RCEB received after the download notification. This
patch handles this RCEB and keeps compatibility with future versions that might
not emit this RCEB.

i1480_rceb_check() is reused to check for the RCEB. It is also refactored with
improved comments and reused in another place in mac.c where the checking was
being duplicated.

This patch was tested on both i1480 and GUWA100U HWAs, with all firmware
versions currently available.

Signed-off-by: Anderson Lizardo <anderson.lizardo@indt.org.br>
diff --git a/drivers/uwb/i1480/dfu/i1480-dfu.h b/drivers/uwb/i1480/dfu/i1480-dfu.h
index 8035418..46f45e8 100644
--- a/drivers/uwb/i1480/dfu/i1480-dfu.h
+++ b/drivers/uwb/i1480/dfu/i1480-dfu.h
@@ -145,7 +145,7 @@
 extern ssize_t i1480_cmd(struct i1480 *, const char *, size_t, size_t);
 extern int i1480_rceb_check(const struct i1480 *,
 			    const struct uwb_rceb *, const char *, u8,
-			    unsigned, unsigned);
+			    u8, unsigned);
 
 enum {
 	/* Vendor specific command type */