am3517_evm: Use ttyS2 instead of ttyO2

The serial driver in the kernel moved from ttyOx to ttySx a while
ago.  This patch updates the console parameter to align with the
kernel change.

Signed-off-by: Adam Ford <aford173@gmail.com>
diff --git a/include/configs/am3517_evm.h b/include/configs/am3517_evm.h
index 4e7e520..eb50012 100644
--- a/include/configs/am3517_evm.h
+++ b/include/configs/am3517_evm.h
@@ -88,7 +88,7 @@
 
 #define CONFIG_EXTRA_ENV_SETTINGS \
 	"loadaddr=0x82000000\0" \
-	"console=ttyO2,115200n8\0" \
+	"console=ttyS2,115200n8\0" \
 	"fdtfile=am3517-evm.dtb\0" \
 	"fdtaddr=0x82C00000\0" \
 	"vram=16M\0" \