dataspaceDetails should not print decimal value

Need to be consistent. Doesn't make sense to print 0
when we don't print the dataspace value for other values.
Leave the printing up to the caller and just return the
string information requested.
Test: adb shell dumpsys SurfaceFlinger
      Look for dataspace details in output
Bug: 63146977

Change-Id: I74f079e6579cfa063a9bd97bdb7c6ac9e75c05b4