MAINTAINERS: add MSM mailing list

Just adds a mailing list to the MSM maintainer entry.
Signed-off-by: NDaniel Walker <dwalker@codeaurora.org>

MAINTAINERS

@@ -814,6 +814,7 @@ ARM/QUALCOMM MSM MACHINE SUPPORT
 M:	David Brown <davidb@codeaurora.org>
 M:	Daniel Walker <dwalker@codeaurora.org>
 M:	Bryan Huntsman <bryanh@codeaurora.org>
+L:	linux-arm-msm@vger.kernel.org
 F:	arch/arm/mach-msm/
 F:	drivers/video/msm/
 F:	drivers/mmc/host/msm_sdcc.c