Use power button to go back in watch themes

Change-Id: I1463a0ba62a23c68c15f05e79a99fa8509314373
Signed-off-by: Vojtech Bocek <vbocek@gmail.com>
diff --git a/gui/devices/240x240/res/ui.xml b/gui/devices/240x240/res/ui.xml
index d157f85..8893669 100644
--- a/gui/devices/240x240/res/ui.xml
+++ b/gui/devices/240x240/res/ui.xml
@@ -272,7 +272,7 @@
 
 			<object type="action">
 				<touch key="power" />
-				<action function="overlay">lock</action>
+				<action function="key">back</action>
 			</object>
 
 			<object type="action">
diff --git a/gui/devices/280x280/res/ui.xml b/gui/devices/280x280/res/ui.xml
index 971e637..d8fec3b 100644
--- a/gui/devices/280x280/res/ui.xml
+++ b/gui/devices/280x280/res/ui.xml
@@ -272,7 +272,7 @@
 
 			<object type="action">
 				<touch key="power" />
-				<action function="overlay">lock</action>
+				<action function="key">back</action>
 			</object>
 
 			<object type="action">
diff --git a/gui/devices/320x320/res/ui.xml b/gui/devices/320x320/res/ui.xml
index 4678e85..ee6a731 100644
--- a/gui/devices/320x320/res/ui.xml
+++ b/gui/devices/320x320/res/ui.xml
@@ -272,7 +272,7 @@
 
 			<object type="action">
 				<touch key="power" />
-				<action function="overlay">lock</action>
+				<action function="key">back</action>
 			</object>
 
 			<object type="action">