Fix leak of FILE* in dumping

Avoid fdopen as fclose, which frees the FILE*, will close
the FD which we don't want. Just normalize on dprintf instead,
and we can add buffering if it turns out to matter at some point

Test: ran 'dumpsys gfxinfo framestats' in a loop while observing PSS
Change-Id: I7808753641aa1055cfdf570c3e017017f11f1dee