Fix getSwitchState.

InputReader::getSwitchState always returns AKEY_STATE_UNKNOWN
because SwitchInputMapper::getSources() returns 0 which cannot
match any source mask including AINPUT_SOURCE_ANY.  As a result
initial lid switch detection is broken.

This change adds a new source constant AINPUT_SOURCE_SWITCH
that indicates that the source has switches.

Change-Id: I5321ecf0ce84f1c2b4535f6c163d3f4dcf9b7a9b
diff --git a/services/input/InputReader.cpp b/services/input/InputReader.cpp
index 8e9a5a4..2e83256 100644
--- a/services/input/InputReader.cpp
+++ b/services/input/InputReader.cpp
@@ -744,7 +744,7 @@
 }
 
 uint32_t SwitchInputMapper::getSources() {
-    return 0;
+    return AINPUT_SOURCE_SWITCH;
 }
 
 void SwitchInputMapper::process(const RawEvent* rawEvent) {