MAINTAINERS: change broken url for prism54

Reported-by: NJoe Perches <joe@perches.com>
Signed-off-by: NJohn W. Linville <linville@tuxdriver.com>

MAINTAINERS

@@ -4549,7 +4549,7 @@ F:	include/linux/preempt.h
 PRISM54 WIRELESS DRIVER
 M:	"Luis R. Rodriguez" <mcgrof@gmail.com>
 L:	linux-wireless@vger.kernel.org
-W:	http://prism54.org
+W:	http://wireless.kernel.org/en/users/Drivers/p54
 S:	Obsolete
 F:	drivers/net/wireless/prism54/