Replace call of celt_inner_prod_c() (step 2)

Should call celt_inner_prod().
This requires the API change of celt_pitch_xcorr() by passing in
"arch".

We tested on x86 and arm, and got bit exact results as original.

Change-Id: I606915da6a196f327ce81f4a5ae32811f4c1fabb

Signed-off-by: Jean-Marc Valin <jmvalin@jmvalin.ca>