tracing: Fix spelling mistake "aritmethic" -> "arithmetic"

There is a spelling mistake in the tracing mini-HOWTO text. Fix it.

Link: https://lkml.kernel.org/r/20211108201513.42876-1-colin.i.king@gmail.comSigned-off-by: Colin Ian King <colin.i.king@gmail.com>
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>

kernel/trace/trace.c

@@ -5635,7 +5635,7 @@ static const char readme_msg[] =
 	"\t        - a numeric literal: e.g. ms_per_sec=1000,\n"
 	"\t        - an arithmetic expression: e.g. time_secs=current_timestamp/1000\n"
 	"\n"
-	"\t    hist trigger aritmethic expressions support addition(+), subtraction(-),\n"
+	"\t    hist trigger arithmetic expressions support addition(+), subtraction(-),\n"
 	"\t    multiplication(*) and division(/) operators. An operand can be either a\n"
 	"\t    variable reference, field or numeric literal.\n"
 	"\n"