Migrate String8|16.setTo to assignment operator

Bug: 295394788
Test: make checkbuild
Change-Id: I370f66c469de73064dec2e42c539dc236dd69d1e
diff --git a/tools/split-select/SplitDescription.cpp b/tools/split-select/SplitDescription.cpp
index 7150008..c02e2d7 100644
--- a/tools/split-select/SplitDescription.cpp
+++ b/tools/split-select/SplitDescription.cpp
@@ -134,10 +134,10 @@
     String8 configStr;
     String8 extensionStr;
     if (index >= 0) {
-        configStr.setTo(str.c_str(), index);
-        extensionStr.setTo(str.c_str() + index + 1);
+        configStr = String8(str.c_str(), index);
+        extensionStr = (str.c_str() + index + 1);
     } else {
-        configStr.setTo(str);
+        configStr = str;
     }
 
     SplitDescription split;