CLEANUP: fix typos in comments for contrib/spoa_example

Fixes 3 common typos in the comments of the contrib/spoa_example
subsystem.

contrib/spoa_example/include/mini-clist.h

@@ -57,7 +57,7 @@ struct list {
 #define LIST_NEXT(lh, pt, el) (LIST_ELEM((lh)->n, pt, el))
 
 
-/* returns a pointer of type <pt> to a structure preceeding the element
+/* returns a pointer of type <pt> to a structure preceding the element
  * which contains list head <lh>, which is known as element <el> in
  * struct pt.
  */

contrib/spoa_example/include/spop_functions.h

@@ -124,7 +124,7 @@ spoe_encode_buffer(const char *str, size_t len, char **buf, char *end)
 /* Encode a buffer, possibly partially. It does the same thing than
  * 'spoe_encode_buffer', but if there is not enough space, it does not fail.
  * On success, it returns the number of copied bytes and <*buf> is moved after
- * the encoded value. If an error occured, it returns -1. */
+ * the encoded value. If an error occurred, it returns -1. */
 static inline int
 spoe_encode_frag_buffer(const char *str, size_t len, char **buf, char *end)
 {
@@ -176,7 +176,7 @@ spoe_decode_buffer(char **buf, char *end, char **str, uint64_t *len)
 
 /* Encode a typed data using value in <data> and type <type>. On success, it
  * returns the number of copied bytes and <*buf> is moved after the encoded
- * value. If an error occured, it returns -1.
+ * value. If an error occurred, it returns -1.
  *
  * If the value is too big to be encoded, depending on its type, then encoding
  * failed or the value is partially encoded. Only strings and binaries can be