tracing/tools: fix a couple of spelling mistakes

There is a spelling mistake in the -g help option, I believe
it should be "graph".  There is also a spelling mistake in a
warning message. Fix both mistakes.

Link: https://lkml.kernel.org/r/20210225165248.22050-2-Viktor.Rosendahl@bmw.de



Signed-off-by: Colin Ian King <colin.king@canonical.com>
Signed-off-by: Viktor Rosendahl <Viktor.Rosendahl@bmw.de>
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>