dm: spi_flash: Allow the uclass to work without printf()

For SPL we don't really need sprintf() and with tiny-printf this is not
available. Allow this to be dropped in SPL when using tiny-printf.

Signed-off-by: Simon Glass <sjg@chromium.org>
diff --git a/drivers/mtd/spi/sf-uclass.c b/drivers/mtd/spi/sf-uclass.c
index 95ffad4..19de964 100644
--- a/drivers/mtd/spi/sf-uclass.c
+++ b/drivers/mtd/spi/sf-uclass.c
@@ -55,11 +55,17 @@
 {
 	struct spi_slave *slave;
 	struct udevice *bus;
-	char name[30], *str;
+	char *str;
 	int ret;
 
+#if defined(CONFIG_SPL_BUILD) && defined(CONFIG_USE_TINY_PRINTF)
+	str = "spi_flash";
+#else
+	char name[30];
+
 	snprintf(name, sizeof(name), "spi_flash@%d:%d", busnum, cs);
 	str = strdup(name);
+#endif
 	ret = spi_get_bus_and_cs(busnum, cs, max_hz, spi_mode,
 				  "spi_flash_std", str, &bus, &slave);
 	if (ret)