drivers/misc/sgi-gru/grukdump.c: unlocking should be conditional in gru_dump_context()

I was reviewing this and noticed that unlocking should be conditional on
the error path.  I've changed it to unlock and return directly since we
only do it once and it seems unlikely to change in the near future.

Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Acked-by: Dimitri Sivanich <sivanich@sgi.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>