avutil/tests/audio_fifo.c: Memory leak and tab space fixes

Prevents memory leak when read_samples_from_audio_fifo() is
called more than once by deallocating before reallocating
more memory.

Fixes space indentation for contents in ERROR().

Signed-off-by: Thomas Turner <thomastdt@googlemail.com>
Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>
