x86: Correct missing local variable in bootm

Enabling FIT produces a compile error. Fix this.

Signed-off-by: Simon Glass <sjg@chromium.org>

arch/x86/lib/bootm.c

@@ -63,6 +63,8 @@ int do_bootm_linux(int flag, int argc, char * const argv[],
 		}
 #if defined(CONFIG_FIT)
 	} else if (images->fit_uname_os) {
+		int ret;
+
 		ret = fit_image_get_data(images->fit_hdr_os,
 					images->fit_noffset_os, &data, &len);
 		if (ret) {