pph: include config.h from rate_speexrate.c

pph: include config.h from rate_speexrate.c

Fixes compilation against libspeexdsp 1.2rc3.

rate_speexrate.c includes speex_resampler.h, which depends on config.h
by referencing the HAVE_SPEEX_SPEEXDSP_TYPES_H macro. AFAIK it's not
a good idea to include config.h from headers (I don't know/remember
why, though), which is why I include config.h from rate_speexrate.c
instead of speex_resampler.h.

Signed-off-by: Tanu Kaskinen <tanuk@iki.fi>
Signed-off-by: Takashi Iwai <tiwai@suse.de>