lavfi/mandelbrot: fix speedloss with default config after morphing introduction.

Morphing was introduced in 0d6e5a171 and forced cos/sin computations
with some mult all the time. This commit makes sure these are computed
only when morphing is enabled.
lavfi/mandelbrot: reindent after 51bcd5cd.
lavfi: always check return value of ff_get_{audio,video}_buffer()

Signed-off-by: Paul B Mahol <onemda@gmail.com>
lavfi/noise: copy inline asm from mp=noise

Signed-off-by: Paul B Mahol <onemda@gmail.com>
lavfi: remove noise libmpcodecs wrapper

Native filter have reached similar performance.

Signed-off-by: Paul B Mahol <onemda@gmail.com>
avfilter/vf_noise: fix build without mmx*inline

Signed-off-by: Michael Niedermayer <michaelni@gmx.at>