ARM: SAMSUNG: Should check for IS_ERR(clk) instead of NULL

On the error condition clk_get() returns ERR_PTR().
Signed-off-by: Jonghwan Choi <jhbird.choi@samsung.com>
Cc: Stable <stable@vger.kernel.org>
Signed-off-by: Kukjin Kim <kgene.kim@samsung.com>

arch/arm/plat-samsung/include/plat/watchdog-reset.h

@@ -25,7 +25,7 @@ static inline void arch_wdt_reset(void)
 
 	__raw_writel(0, S3C2410_WTCON);	  /* disable watchdog, to be safe  */
 
-	if (s3c2410_wdtclk)
+	if (!IS_ERR(s3c2410_wdtclk))
 		clk_enable(s3c2410_wdtclk);
 
 	/* put initial values into count and data */