MAINTAINERS: update Broadcom BCMBCA maintainer

Joel is no longer with Broadcom. Remove his email from bcmbca maintainer
list and replace him with myself for stack protection maintainer.

Signed-off-by: William Zhang <william.zhang@broadcom.com>

MAINTAINERS

@@ -224,7 +224,6 @@ ARM BROADCOM BCMBCA
 M:	Anand Gore <anand.gore@broadcom.com>
 M:	William Zhang <william.zhang@broadcom.com>
 M:	Kursad Oney <kursad.oney@broadcom.com>
-M:	Joel Peshkin <joel.peshkin@broadcom.com>
 M:	Philippe Reynes <philippe.reynes@softathome.com>
 S:	Maintained
 F:	arch/arm/mach-bcmbca/
@@ -1568,7 +1567,7 @@ F:	cmd/sqfs.c
 F:	test/py/tests/test_fs/test_squashfs/
 
 STACKPROTECTOR
-M:	Joel Peshkin <joel.peshkin@broadcom.com>
+M:	William Zhang <william.zhang@broadcom.com>
 S:	Maintained
 F:	common/stackprot.c
 F:	cmd/stackprot_test.c