[doc, style] Make C coding style public API example more clear

The example should be sufficient to be able to adapt without the need
of visiting doxygen documentation.

"@p arg1" is misleading, whilst "@p pots_of_gold" matches the doxygen
style exactly.

Signed-off-by: Silvestrs Timofejevs <silvestrst@lowrisc.org>
diff --git a/doc/rm/c_cpp_coding_style.md b/doc/rm/c_cpp_coding_style.md
index ba8c7d5..45e24b0 100644
--- a/doc/rm/c_cpp_coding_style.md
+++ b/doc/rm/c_cpp_coding_style.md
@@ -120,8 +120,8 @@
 /**
  * Do something amazing
  *
- * Create a rainbow and place a unicorn at the bottom of it. @p arg1 pots of
- * gold will be positioned on the east end of the rainbow.
+ * Create a rainbow and place a unicorn at the bottom of it. @p pots_of_gold
+ * pots of gold will be positioned on the east end of the rainbow.
  *
  * @param pots_of_gold Number of gold pots to place next to the rainbow
  * @param unicorns Number of unicorns to position on the rainbow