mcd-account.c:2175:12: error: this statement may fall through [-Werror=implicit-fallthrough=]

Compilation failure: src/mcd-account.c

```
mcd-account.c: In function ‘mc_param_type’:
mcd-account.c:2175:12: error: this statement may fall through [-Werror=implicit-fallthrough=]
 2175 |         if (dbus_signature[1] == DBUS_TYPE_STRING)
      |            ^
mcd-account.c:2182:5: note: here
 2182 |     default:

```