Commit 17e88bf0 created a memleak by
removing a call to ff_iir_filter_free_coeffsp on error; this has been
found by Coverity (ID 1464159). This commit fixes the memleak by
readding the call to ff_iir_filter_free_coeffsp.

Notice that this is not a simple revert, because several macros that
were used before 17e88bf0 were replaced
in commit 44863b2c and completely removed
in 2658680d.
Reviewed-by: Limin Wang <lance.lmwang@gmail.com>
Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt@gmail.com>