avcodec/alacenc: Don't free unnecessarily

avcodec/alacenc: Don't free unnecessarily

The init function of the ALAC encoder calls its own close function
if a call to ff_lpc_init() fails; yet nothing has been allocated before
that point (except extradata which is freed generically) and ff_lpc_init()
can be expected to clean up after itself on error (the documentation does
not say anything to the contrary and the current implementation can only
fail if the only allocation fails, so there is nothing to clean up on
error anyway), so this is unnecessary.

Reviewed-by: Paul B Mahol <onemda@gmail.com>
Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt@gmail.com>