Resolve "MSAN: use-of-uninitialized-value in tcx_utils_enc_fx.c:3808:5"

• Related issues: #2470 (closed)
• Requested reviewers: @kiene

Reason why this change is needed

• powerSpec_e might now always be initialized in core_signal_analysis_high_bitrate_fx(); for example, in case of TCX5

Description of the change

• Make sure to properly initialize powerSpec_e

Affected operating points

• All operating points are BE, since it is actually never really used uninitialized.

Closes #2470 (closed)