kgdbts: fix hw_access_break_test

kgdbts: fix hw_access_break_test

The test for access watchpoints (hw_access_break_test) was broken
(always failed) because the compiler optimized out the write to the
static helper variable (hw_break_val2), as it is never read anywhere.
This resulted in the target variable (hw_break_val) not being accessed
and thus the breakpoint not being triggered.

Remove the helper variable (hw_break_val2), and use READ_ONCE to force
reading the target variable (hw_break_val).

Signed-off-by: Florian Rommel <mail@florommel.de>
Reviewed-by: Douglas Anderson <dianders@chromium.org>
Link: https://lore.kernel.org/r/20240812085459.291741-1-mail@florommel.de
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>