acpi/nfit: Fix COMPLETION_INITIALIZER_ONSTACK() abuse

COMPLETION_INITIALIZER_ONSTACK() is supposed to be used as an initializer,
in other words, it should only be used in assignment expressions or
compound literals. So the usage in drivers/acpi/nfit/core.c:

COMPLETION_INITIALIZER_ONSTACK(flush.cmp);

... is inappropriate.

Besides, this usage could also break the build for another fix that
reduces stack sizes caused by COMPLETION_INITIALIZER_ONSTACK(), because
that fix changes COMPLETION_INITIALIZER_ONSTACK() from rvalue to lvalue,
and usage as above will report the following error:

drivers/acpi/nfit/core.c: In function 'acpi_nfit_flush_probe':
include/linux/completion.h:77:3: error: value computed is not used [-Werror=unused-value]
(*({ init_completion(&work); &work; }))

This patch fixes this by replacing COMPLETION_INITIALIZER_ONSTACK()
with init_completion() in acpi_nfit_flush_probe(), which does the
same initialization without any other problems.

Signed-off-by: Boqun Feng <[e-mail]>
Signed-off-by: Peter Zijlstra (Intel) <[e-mail]>
Acked-by: Dan Williams <[e-mail]>
Acked-by: Arnd Bergmann <[e-mail]>
Cc: Andrew Morton <[e-mail]>
Cc: Byungchul Park <[e-mail]>
Cc: Len Brown <[e-mail]>
Cc: Linus Torvalds <[e-mail]>
Cc: Nicholas Piggin <[e-mail]>
Cc: Peter Zijlstra <[e-mail]>
Cc: Rafael J. Wysocki <[e-mail]>
Cc: Thomas Gleixner <[e-mail]>
Cc: [e-mail]
Cc: [e-mail]
Link: http://lkml.kernel.org/r/[e-mail]
Signed-off-by: Ingo Molnar <[e-mail]>

drivers/acpi/nfit/core.c

···
 	 * need to be interruptible while waiting.
 	 */
 	INIT_WORK_ONSTACK(&flush.work, flush_probe);
-	COMPLETION_INITIALIZER_ONSTACK(flush.cmp);
+	init_completion(&flush.cmp);
 	queue_work(nfit_wq, &flush.work);
 	mutex_unlock(&acpi_desc->init_mutex);