power/sysrq: fix inconstistent help message of sysrq key

Currently help message of /proc/sysrq-trigger highlight its
upper-case characters, like below:

      SysRq : HELP : loglevel(0-9) reBoot Crash terminate-all-tasks(E)
      memory-full-oom-kill(F) kill-all-tasks(I) ...

this would confuse user trigger sysrq by upper-case character, which is
inconsistent with the real lower-case character registed key.

This inconsistent help message will also lead more confused when
26 upper-case letters put into use in future.

This patch fix power off sysrq key: "poweroff(o)"

Signed-off-by: zhangwei(Jovi) <jovi.zhangwei@huawei.com>
Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

kernel/power/poweroff.c

@@ -32,7 +32,7 @@ static void handle_poweroff(int key)
 
 static struct sysrq_key_op	sysrq_poweroff_op = {
 	.handler        = handle_poweroff,
-	.help_msg       = "powerOff",
+	.help_msg       = "poweroff(o)",
 	.action_msg     = "Power Off",
 	.enable_mask	= SYSRQ_ENABLE_BOOT,
 };