clk: ti: check for null return in strrchr to avoid null dereferencing

strrchr can potentially return a null so the following strlen on the
null pointer can cause a null dereference. Add a check to see if
the string postfix is not null before calling strlen.

Detected by CoverityScan, CID#1452039 ("Dereference null return")

Signed-off-by: Colin Ian King <colin.king@canonical.com>
Acked-by: Tero Kristo <t-kristo@ti.com>
Signed-off-by: Stephen Boyd <sboyd@codeaurora.org>

drivers/clk/ti/adpll.c

@@ -222,7 +222,7 @@ static int ti_adpll_setup_clock(struct ti_adpll_data *d, struct clk *clock,
 
 	/* Separate con_id in format "pll040dcoclkldo" to fit MAX_CON_ID */
 	postfix = strrchr(name, '.');
-	if (strlen(postfix) > 1) {
+	if (postfix && strlen(postfix) > 1) {
 		if (strlen(postfix) > ADPLL_MAX_CON_ID)
 			dev_warn(d->dev, "clock %s con_id lookup may fail\n",
 				 name);