drivers/misc/sgi-gru/grufile.c: fix the wrong members of gru_chip

Fix the wrong members and the wrong function's definition, since the
irq_chip had changed.

Signed-off-by: Wanlong Gao <wanlong.gao@gmail.com>
Cc: Jack Steiner <steiner@sgi.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>