MIPS: Fix build error if CONFIG_CEVT_R4K is undefined.

Introduced by 99aa5029937ee926e3b249369e208d7013cd381b.
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>

arch/mips/include/asm/time.h

@@ -61,7 +61,7 @@ static inline int mips_clockevent_init(void)
 	extern int smtc_clockevent_init(void);
 
 	return smtc_clockevent_init();
-#elif CONFIG_CEVT_R4K
+#elif defined(CONFIG_CEVT_R4K)
 	return r4k_clockevent_init();
 #else
 	return -ENXIO;