tracing/histogram: Update division by 0 documentation

If the divisor is a constant and zero, the undeifned case can be
detected and an error returned instead of -1.

Link: https://lkml.kernel.org/r/[email protected]

Cc: Jonathan Corbet <[email protected]>
Cc: Ingo Molnar <[email protected]>
Cc: Shuah Khan <[email protected]>
Cc: Tom Zanussi <[email protected]>
Signed-off-by: Kalesh Singh <[email protected]>
Signed-off-by: Steven Rostedt (VMware) <[email protected]>

Author: Kalesh Singh

Documentation/trace/histogram.rst

@@ -1766,7 +1766,8 @@ using the same key and variable from yet another event::
 Expressions support the use of addition, subtraction, multiplication and
 division operators (+-\*/).
 
-Note that division by zero always returns -1.
+Note if division by zero cannot be detected at parse time (i.e. the
+divisor is not a constant), the result will be -1.
 
 Numeric constants can also be used directly in an expression::