Use srsran_convert_dB_to_power

Instead of computing power using the power function.

lib/src/phy/phch/test/npdsch_npdcch_file_test.c

@@ -213,7 +213,7 @@ int main(int argc, char** argv)
 
       // add some noise to the signal
       if (snr != -1.0) {
-        float var = powf(10.0f, -snr / 10.0f);
+        float var = srsran_convert_dB_to_power(-snr);
         srsran_ch_awgn_c(buff_ptrs[0], buff_ptrs[0], var, nread);
       }
 

lib/src/phy/sync/test/sync_sl_test.c

@@ -166,7 +166,7 @@ int main(int argc, char** argv)
 
     // ADD CHANNEL NOISE
     if (snr < 50) {
-      float var = powf(10.0f, -snr / 10.0f);
+      float var = srsran_convert_dB_to_power(-snr);
       srsran_ch_awgn_c(output_buffer, output_buffer, var, output_buffer_len);
     }