arm: fft_vfp: Add a missing "endconst" when building in thumb mode

Signed-off-by: Martin Storsjö <martin@martin.st>
arm: fft_vfp: Unify the behaviour in ff_fft_calc_vfp between arm/thumb

Don't include the function pointer table in the code segment
in arm mode.

This shouldn't have any significant performance effect. It does
end up as a few more instructions than before, for ARM, but
only at the entry to this function, not within the fft functions
themselves.

Signed-off-by: Martin Storsjö <martin@martin.st>