[gdb/rust] Add missing _() for error call

In commit 1390b65a1b9 ("[gdb/rust] Fix literal truncation") I forgot to add
_() around a string using in an error call.

Fix this by adding the missing _().

Tested on x86_64-linux.
diff --git a/gdb/rust-parse.c b/gdb/rust-parse.c
index 836f491..f5eb63e 100644
--- a/gdb/rust-parse.c
+++ b/gdb/rust-parse.c
@@ -1027,7 +1027,7 @@ rust_parser::lex_number ()
       const char *trailer;
       value = strtoulst (number.c_str () + offset, &trailer, radix);
       if (*trailer != '\0')
-	error ("Integer literal is too large");
+	error (_("Integer literal is too large"));
       if (implicit_i32 && value >= ((uint64_t) 1) << 31)
 	type = get_type ("i64");