arch: m68k: Use existing CONFIG_MCFTMR instead of CFG_MCFTMR

There is an existing CONFIG_MCFTMR Kconfig symbol,
use it and drop all other instances of CFG_MCFTMR.
This duality is likely a result of bogus conversion
to Kconfig.

Fixes: 7ff7b46e6ce ("m68k: rename CONFIG_MCFTMR to CFG_MCFTMR")
Signed-off-by: Marek Vasut <marek.vasut+renesas@mailbox.org>
diff --git a/arch/m68k/lib/time.c b/arch/m68k/lib/time.c
index ca8c039..500e4db 100644
--- a/arch/m68k/lib/time.c
+++ b/arch/m68k/lib/time.c
@@ -25,7 +25,7 @@
 #define CFG_SYS_WATCHDOG_FREQ (CONFIG_SYS_HZ / 2)
 #endif
 
-#if defined(CFG_MCFTMR)
+#if CONFIG_IS_ENABLED(MCFTMR)
 #ifndef CFG_SYS_UDELAY_BASE
 #	error	"uDelay base not defined!"
 #endif
@@ -111,7 +111,7 @@
 	return (timestamp - base);
 }
 
-#endif				/* CFG_MCFTMR */
+#endif				/* CONFIG_MCFTMR */
 
 /*
  * This function is derived from PowerPC code (read timebase as long long).