cmd: fdt: Handle 64bit pointers in fdt get addr

The command assumed 32bit pointers so far, with 64bit pointer the
command would overwrite a piece of stack. Fix it by extending the
array size to cater for 64bit pointer, and use snprintf() to avoid
writing past the end of the array ever again.

Signed-off-by: Marek Vasut <marek.vasut+renesas@mailbox.org>
Reviewed-by: Simon Glass <sjg@chromium.org>
diff --git a/cmd/fdt.c b/cmd/fdt.c
index 279dad9..bc19303 100644
--- a/cmd/fdt.c
+++ b/cmd/fdt.c
@@ -466,9 +466,9 @@
 						return ret;
 				} else if (subcmd[0] == 'a') {
 					/* Get address */
-					char buf[11];
+					char buf[19];
 
-					sprintf(buf, "0x%p", nodep);
+					snprintf(buf, sizeof(buf), "0x%p", nodep);
 					env_set(var, buf);
 				} else if (subcmd[0] == 's') {
 					/* Get size */