MAINTAINERS: target/mips: Add filter for mips in email subjects

Add ability to redirect mails (sent to qemu-devel) containing
"mips" in the subject line to MIPS maintainers and reviewers.
Reviewed-by: NPhilippe Mathieu-Daudé <philmd@redhat.com>
Signed-off-by: NAleksandar Markovic <amarkovic@wavecomp.com>

MAINTAINERS

@@ -221,6 +221,7 @@ F: tests/tcg/mips/
 F: disas/mips.c
 F: disas/nanomips.h
 F: disas/nanomips.cpp
+K: ^Subject:.*(?i)mips
 
 Moxie
 M: Anthony Green <green@moxielogic.com>