arm/digic: replace snprintf() with g_strdup_printf()

arm/digic: replace snprintf() with g_strdup_printf()

Also fixes a GCC 12.0.1 false-positive:
../hw/arm/digic.c: In function ‘digic_init’:
../hw/arm/digic.c:45:54: error: ‘%d’ directive output may be truncated writing between 1 and 11 bytes into a region of size 5 [-Werror=format-truncation=]
   45 |         snprintf(name, DIGIC_TIMER_NAME_MLEN, "timer[%d]", i);
      |                                                      ^~

Signed-off-by: Marc-André Lureau <marcandre.lureau@redhat.com>
Reviewed-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Daniel P. Berrangé <berrange@redhat.com>
Message-Id: <20220420132624.2439741-14-marcandre.lureau@redhat.com>