greybus: svc: Fix build warning on 64bit systems

Fix below warnings that only generate for a 64 bit system:

greybus/svc.c:202:16: warning: format ‘%d’ expects argument of type ‘int’, but argument 4 has type ‘size_t {aka long unsigned int}’ [-Wformat=]
   dev_err(dev, "%s: Illegal size of hello request (%d %d)\n",
                ^
greybus/svc.c:202:16: warning: format ‘%d’ expects argument of type ‘int’, but argument 5 has type ‘long unsigned int’ [-Wformat=]

Fixes: 9cbe73e0cf45 ("svc: Implement SVC requests")
Reported-by: Greg KH <gregkh@google.com>
Signed-off-by: Viresh Kumar <viresh.kumar@linaro.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@google.com>