MAINTAINERS: update SGI & ia64 Altix stuff

Dimitri and Robin have taken over GRU maintenance.

Linux on Altix is no longer maintained except as part of ia64, and
there's already a separate IA64 maintainer entry.
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Signed-off-by: Tony Luck <tony.luck@intel.com>

MAINTAINERS

@@ -6768,7 +6768,8 @@ S:	Supported
 F:	drivers/net/ethernet/sfc/
 
 SGI GRU DRIVER
-M:	Jack Steiner <steiner@sgi.com>
+M:	Dimitri Sivanich <sivanich@sgi.com>
+M:	Robin Holt <holt@sgi.com>
 S:	Maintained
 F:	drivers/misc/sgi-gru/
 
@@ -6963,14 +6964,6 @@ L:	linux-fbdev@vger.kernel.org
 S:	Maintained
 F:	drivers/video/smscufx.c
 
-SN-IA64 (Itanium) SUB-PLATFORM
-M:	Jes Sorensen <jes@sgi.com>
-L:	linux-altix@sgi.com
-L:	linux-ia64@vger.kernel.org
-W:	http://www.sgi.com/altix
-S:	Maintained
-F:	arch/ia64/sn/
-
 SOC-CAMERA V4L2 SUBSYSTEM
 M:	Guennadi Liakhovetski <g.liakhovetski@gmx.de>
 L:	linux-media@vger.kernel.org