doc: fix build with sphinx 4.5

[ upstream commit fe45ccd ]

Latest Sphinx checks C language syntax more aggressively.
Fix the following warning by correcting C language syntax.

doc/guides/prog_guide/event_ethernet_rx_adapter.rst:243:
WARNING: Could not lex literal_block as "c". Highlighting skipped.

Fixes: 3c83806 ("eventdev: introduce event vector Rx capability")

Signed-off-by: Jerin Jacob <jerinj@marvell.com>
Acked-by: Jay Jayatheerthan <jay.jayatheerthan@intel.com>

doc/guides/prog_guide/event_ethernet_rx_adapter.rst

@@ -257,8 +257,8 @@ A loop processing ``rte_event_vector`` containing mbufs is shown below.
                         /* Process each mbuf. */
                 }
         break;
-        case ...
-        ...
+        case default:
+                /* Handle other event_types. */
         }
 
 Rx event vectorization for SW Rx adapter