linux-aspeed: Move to 5.1.15

This includes security and bug fixes from the 5.1.13, 5.1.14 and 5.1.15
stable releases.

Change-Id: I6cda770a288e96d77bfcb78a53a8fe07bf746c49
Signed-off-by: Joel Stanley <joel@jms.id.au>
diff --git a/recipes-kernel/linux/linux-aspeed_git.bb b/recipes-kernel/linux/linux-aspeed_git.bb
index dc3073d..6539508 100644
--- a/recipes-kernel/linux/linux-aspeed_git.bb
+++ b/recipes-kernel/linux/linux-aspeed_git.bb
@@ -1,6 +1,6 @@
 KBRANCH ?= "dev-5.1"
-LINUX_VERSION ?= "5.1.12"
+LINUX_VERSION ?= "5.1.15"
 
-SRCREV="72dc92286966c86e8fa6039922eb510ce27e20c2"
+SRCREV="815857a6057057faa3a0dcf2d7df03f305361550"
 
 require linux-aspeed.inc