equalizer: Enforce type correctness for M_PI as well

It was my expectation that M_PI in the EqzCoeffs function is automatically cast
to a float during compile time, but my expectation turned out to be incorrect.
Specifically, I noticed in GCC's assembly output of equalizer.c that GCC was
doing the inverse by making the program convert all single-precision terms
(excluding 2.0f * M_PI) in the line containing M_PI to double-precision, and
then making it convert the double-precision result to single-precision before
the assignment to f_theta_1.  As a result, M_PI must be explicitly cast to a
float.
Signed-off-by: Jean-Baptiste Kempf <jb@videolan.org>

modules/audio_filter/equalizer.c

@@ -254,7 +254,7 @@ static void EqzCoeffs( int i_rate, float f_octave_percent,
 
         if( f_freq <= f_nyquist_freq )
         {
-            float f_theta_1 = ( 2.0f * M_PI * f_freq ) / f_rate;
+            float f_theta_1 = ( 2.0f * (float) M_PI * f_freq ) / f_rate;
             float f_theta_2 = f_theta_1 / f_octave_factor;
             float f_sin     = sinf( f_theta_2 );
             float f_sin_prd = sinf( f_theta_2 * f_octave_factor_1 )