MIPS: alchemy: cpu_all_mask is forbidden for clock event devices

change alchemy clock event device cpu_all_mask to cpu_possible_mask.
Gets rid of a warning, which then does the same substitution:
WARNING: CPU: 0 PID: 0 at kernel/time/clockevents.c:468 clockevents_register_device+0x130/0x140
rtcmatch2 cpumask == cpu_all_mask, using cpu_possible_mask instead

Signed-off-by: Manuel Lauss <[e-mail]>
Signed-off-by: Paul Burton <[e-mail]>
Cc: Linux-MIPS <[e-mail]>

arch/mips/alchemy/common/time.c

···
 	.features	= CLOCK_EVT_FEAT_ONESHOT,
 	.rating		= 1500,
 	.set_next_event = au1x_rtcmatch2_set_next_event,
-	.cpumask	= cpu_all_mask,
+	.cpumask	= cpu_possible_mask,
 };
 
 static struct irqaction au1x_rtcmatch2_irqaction = {