fdt: Check for NULL return from fdt_getprop in 'fdt set'

While the previous pass through fixed one place where we knew that
fdt_getprop would be given a positive len, in the case of 'fdt set' we
do not, so check that we did no get NULL from fdt_getprop().

Cc: Simon Glass <sjg@chromium.org>
Reported-by: Coverity (CID: 163249)
Fixes 72c98ed1ab ("fdt: Add a check to do_fdt() for coverity")
Signed-off-by: Tom Rini <trini@konsulko.com>
Reviewed-by: Simon Glass <sjg@chromium.org>

cmd/fdt.c

@@ -284,6 +284,10 @@ static int do_fdt(cmd_tbl_t *cmdtp, int flag, int argc, char * const argv[])
 			len = 0;
 		} else {
 			ptmp = fdt_getprop(working_fdt, nodeoffset, prop, &len);
+			if (!ptmp) {
+				printf("prop (%s) not found!\n", prop);
+				return 1;
+			}
 			if (len > SCRATCHPAD) {
 				printf("prop (%d) doesn't fit in scratchpad!\n",
 				       len);