dtc: Fix memory leak in character literal parsing

The data struct used for parsing character literals was never freed
resulting in a few bytes leaked for every character.

Signed-off-by: Gabriel Smith <ga29smith@gmail.com>
Signed-off-by: David Gibson <david@gibson.dropbear.id.au>

dtc-lexer.l

@@ -189,16 +189,16 @@ static void lexical_error(const char *fmt, ...);
 			if (d.len == 1) {
 				lexical_error("Empty character literal");
 				yylval.integer = 0;
-				return DT_CHAR_LITERAL;
-			}
-
+			} else {
 				yylval.integer = (unsigned char)d.val[0];
 
 				if (d.len > 2)
 					lexical_error("Character literal has %d"
 						      " characters instead of 1",
 						      d.len - 1);
+			}
 
+			data_free(d);
 			return DT_CHAR_LITERAL;
 		}