x86: pxeboot: bugfix: Set variable for size of initrd

The problem was, that zboot() didn't work because of missing
ramdisc size.

Signed-off-by: Thomas Mittelstaedt <thomas.mittelstaedt@de.bosch.com>
Reviewed-by: Simon Glass <sjg@chromium.org>
diff --git a/boot/pxe_utils.c b/boot/pxe_utils.c
index ac1414a..a92bb89 100644
--- a/boot/pxe_utils.c
+++ b/boot/pxe_utils.c
@@ -554,7 +554,7 @@
 			       label->name);
 			goto cleanup;
 		}
-
+		strcpy(initrd_filesize, simple_xtoa(size));
 		initrd_addr_str = env_get("ramdisk_addr_r");
 		size = snprintf(initrd_str, sizeof(initrd_str), "%s:%lx",
 				initrd_addr_str, size);