libqcdm,commands: fix warnings with -Wswitch-default

commands.c: In function ‘nv_mode_pref_from_qcdm’:
  commands.c:109:5: warning: switch missing default case [-Wswitch-default]
    109 |     switch (qcdm) {
        |     ^~~~~~

libqcdm/src/commands.c

@@ -135,6 +135,8 @@ nv_mode_pref_from_qcdm (uint8_t qcdm)
         return DIAG_NV_MODE_PREF_GSM_UMTS_LTE_ONLY;
     case QCDM_CMD_NV_MODE_PREF_ITEM_MODE_PREF_1X_HDR_LTE_ONLY:
         return DIAG_NV_MODE_PREF_1X_HDR_LTE_ONLY;
+    default:
+        break;
     }
     return DIAG_NV_MODE_PREF_AUTO;
 };