kgdb/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 kgdb sysrq key: "debug(g)"
Signed-off-by: Nzhangwei(Jovi) <jovi.zhangwei@huawei.com>
Cc: Jason Wessel <jason.wessel@windriver.com>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

kernel/debug/debug_core.c

@@ -775,7 +775,7 @@ static void sysrq_handle_dbg(int key)
 
 static struct sysrq_key_op sysrq_dbg_op = {
 	.handler	= sysrq_handle_dbg,
-	.help_msg	= "debug(G)",
+	.help_msg	= "debug(g)",
 	.action_msg	= "DEBUG",
 };
 #endif