MAINTAINERS: update web URL for iwlwifi

The current URL mentioned in iwlwifi's W entry is outdated and
currently pointing to a dead link. Change it so that it points to the
correct Wiki page directly.

Signed-off-by: Luca Coelho <[e-mail]>
Signed-off-by: Kalle Valo <[e-mail]>

MAINTAINERS

···
 M:	Luca Coelho <[e-mail]>
 M:	Intel Linux Wireless <[e-mail]>
 L:	[e-mail]
-W:	http://intellinuxwireless.org
+W:	https://wireless.wiki.kernel.org/en/users/drivers/iwlwifi
 T:	git git://git.kernel.org/pub/scm/linux/kernel/git/iwlwifi/iwlwifi.git
 S:	Supported
 F:	drivers/net/wireless/intel/iwlwifi/