kdb: Merge identical case statements in kdb_read()

The code that handles case 14 (down) and case 16 (up) has been copy and
pasted despite being byte-for-byte identical. Combine them.

Cc: stable@vger.kernel.org # Not a bug fix but it is needed for later bug fixes
Reviewed-by: Douglas Anderson <dianders@chromium.org>
Tested-by: Justin Stitt <justinstitt@google.com>
Link: https://lore.kernel.org/r/20240424-kgdb_read_refactor-v3-4-f236dbe9828d@linaro.org
Signed-off-by: Daniel Thompson <daniel.thompson@linaro.org>

Author: Daniel Thompson

kernel/debug/kdb/kdb_io.c

@@ -317,6 +317,7 @@ static char *kdb_read(char *buffer, size_t bufsize)
 		}
 		break;
 	case 14: /* Down */
+	case 16: /* Up */
 		memset(tmpbuffer, ' ',
 		       strlen(kdb_prompt_str) + (lastchar-buffer));
 		*(tmpbuffer+strlen(kdb_prompt_str) +
@@ -331,15 +332,6 @@ static char *kdb_read(char *buffer, size_t bufsize)
 			++cp;
 		}
 		break;
-	case 16: /* Up */
-		memset(tmpbuffer, ' ',
-		       strlen(kdb_prompt_str) + (lastchar-buffer));
-		*(tmpbuffer+strlen(kdb_prompt_str) +
-		  (lastchar-buffer)) = '\0';
-		kdb_printf("\r%s\r", tmpbuffer);
-		*lastchar = (char)key;
-		*(lastchar+1) = '\0';
-		return lastchar;
 	case 9: /* Tab */
 		if (tab < 2)
 			++tab;