gdbstub: Adjust gdb_syscall_complete_cb declaration

Change 'ret' to uint64_t.  This resolves a FIXME in the
m68k and nios2 semihosting that we've lost data.
Change 'err' to int.  There is nothing target-specific
about the width of the errno value.

Reviewed-by: Luc Michel <lmichel@kalray.eu>
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
diff --git a/gdbstub.c b/gdbstub.c
index f3a4664..cf869b1 100644
--- a/gdbstub.c
+++ b/gdbstub.c
@@ -1878,11 +1878,12 @@
 static void handle_file_io(GArray *params, void *user_ctx)
 {
     if (params->len >= 1 && gdbserver_state.current_syscall_cb) {
-        target_ulong ret, err;
+        uint64_t ret;
+        int err;
 
-        ret = (target_ulong)get_param(params, 0)->val_ull;
+        ret = get_param(params, 0)->val_ull;
         if (params->len >= 2) {
-            err = (target_ulong)get_param(params, 1)->val_ull;
+            err = get_param(params, 1)->val_ull;
         } else {
             err = 0;
         }