Fix sdk lib impl lib collection in platform_bootclasspath

https://r.android.com/2757569 accidentally led to visiting the sdk
library impl lib direct deps with the wrong dependency tag, leading to
the transitive source files not being properly collected in the
generated srcjar file in platform bootclasspath. This change fixes the
issue by collecting the dependency using the correct tag.

Test: go test ./java
Change-Id: I1be37be1af7b13860d5c0ec99c3567100e5158bd
diff --git a/java/platform_bootclasspath.go b/java/platform_bootclasspath.go
index d09a02e..152eb1e 100644
--- a/java/platform_bootclasspath.go
+++ b/java/platform_bootclasspath.go
@@ -172,7 +172,7 @@
 	// Do not add implLibModule to allModules as the impl lib is only used to collect the
 	// transitive source files
 	var implLibModule []android.Module
-	ctx.VisitDirectDepsWithTag(implLibraryTag, func(m android.Module) {
+	ctx.VisitDirectDepsWithTag(platformBootclasspathImplLibDepTag, func(m android.Module) {
 		implLibModule = append(implLibModule, m)
 	})