lockup_detector: Fix forgotten config conversion

Fix forgotten CONFIG_DETECT_SOFTLOCKUP -> CONFIG_LOCKUP_DETECTOR
in sched.h

Fixes:
	arch/x86/built-in.o: In function `touch_nmi_watchdog':
	(.text+0x1bd59): undefined reference to `touch_softlockup_watchdog'
	kernel/built-in.o: In function `show_state_filter':
	(.text+0x10d01): undefined reference to `touch_all_softlockup_watchdogs'
	kernel/built-in.o: In function `sched_clock_idle_wakeup_event':
	(.text+0x362f9): undefined reference to `touch_softlockup_watchdog'
	kernel/built-in.o: In function `timekeeping_resume':
	timekeeping.c:(.text+0x38757): undefined reference to `touch_softlockup_watchdog'
	kernel/built-in.o: In function `tick_nohz_handler':
	tick-sched.c:(.text+0x3e5b9): undefined reference to `touch_softlockup_watchdog'
	kernel/built-in.o: In function `tick_sched_timer':
	tick-sched.c:(.text+0x3e671): undefined reference to `touch_softlockup_watchdog'
	kernel/built-in.o: In function `tick_check_idle':
	(.text+0x3e90b): undefined reference to `touch_softlockup_watchdog'

Signed-off-by: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Don Zickus <dzickus@redhat.com>
Cc: Ingo Molnar <mingo@elte.hu>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Cyrill Gorcunov <gorcunov@gmail.com>
Cc: Eric Paris <eparis@redhat.com>
Cc: Randy Dunlap <randy.dunlap@oracle.com>