add a missing default case to hmac_drbg_interface

[mojtaba-bisheh]

There is a missing "default case" to caliptra-rtl/src/ecc/rtl/ecc_hmac_drbg_interface.sv line 220 found by FPV team.
The following fix has been implemented internally to address this issue:

            if (hmac_done_edge) begin
                unique case (state_reg) inside
                    LFSR_ST:        lfsr_seed_reg   <= hmac_drbg_result[147 : 0];
                    LAMBDA_ST:      lambda_reg      <= hmac_drbg_result;
                    SCALAR_RND_ST:  scalar_rnd_reg  <= hmac_drbg_result;
                    MASKING_RND_ST: masking_rnd_reg <= hmac_drbg_result;
                    KEYGEN_ST:      drbg_reg        <= hmac_drbg_result;
                    SIGN_ST:        drbg_reg        <= hmac_drbg_result;
                    default: begin
                        lambda_reg <= '0;
                        scalar_rnd_reg <= '0;
                        masking_rnd_reg <= '0;
                        drbg_reg <= '0;
                        lfsr_seed_reg <= LFSR_INIT_SEED;
                    end
                endcase
            end

[calebofearth]

Note: The merge of this fix to the public repo is in progress:
e90baa9

[mojtaba-bisheh]

#240 fixed this.