chore(libc): clean up includes in lib/libc/printf.c

stddef.h is needed for the definition of size_t
stdio.h is needed for the declaration of putchar

Signed-off-by: Jorge Troncoso <jatron@google.com>
Change-Id: I72dac843dbbfc440cff0f9e9d13669b78a812abc
1 file changed