defer/hazptr: Fix line number reference in Section 9.3 Hazard Pointers

The text incorrectly stated that 'line 8 finds' the pointer condition,
but in Listing 9.4, line 7 contains the if statement that performs
the check, while line 8 contains the return statement.

This commit:
1. Adds a label (htr:check) to the if statement on line 7
2. Updates the text to reference the if check (htr:check) instead of
   the return statement (htr:race1) for the condition check
3. Clarifies that the if check finds the condition and the return
   statement returns the value

This makes the description more accurate and reflects the actual
code execution flow.

Signed-off-by: Kunwu Chan <kunwu.chan@linux.dev>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
2 files changed