misc: Doxygen tweaks: fixed some typos and minor errors

Doxygen generates quite a lot of warnings on libosmocore. Some of them
are obvious typos - this patch aims to fix such low-hanging fruit.
diff --git a/include/osmocom/core/statistics.h b/include/osmocom/core/statistics.h
index 04816c1..ade0074 100644
--- a/include/osmocom/core/statistics.h
+++ b/include/osmocom/core/statistics.h
@@ -34,7 +34,7 @@
 struct osmo_counter *osmo_counter_alloc(const char *name);
 
 /*! \brief Free the specified counter
- *  \param[ctr] Counter
+ *  \param[in] ctr Counter
  */
 void osmo_counter_free(struct osmo_counter *ctr);