MAINTAINERS: Update git tree for Broadcom iProc SoCs

Current git tree for Broadcom iProc SoCs is pretty outdated as it has
not updated for a long time. Fix the reference.
Signed-off-by: Kuldeep Singh <singh.kuldeep87k@gmail.com>

MAINTAINERS

@@ -3900,7 +3900,7 @@ M:	Scott Branden <sbranden@broadcom.com>
 M:	bcm-kernel-feedback-list@broadcom.com
 L:	linux-arm-kernel@lists.infradead.org (moderated for non-subscribers)
 S:	Maintained
-T:	git git://github.com/broadcom/cygnus-linux.git
+T:	git git://github.com/broadcom/stblinux.git
 F:	arch/arm64/boot/dts/broadcom/northstar2/*
 F:	arch/arm64/boot/dts/broadcom/stingray/*
 F:	drivers/clk/bcm/clk-ns*