tools/rv: Fix substring match bug in monitor name search

tools/rv: Fix substring match bug in monitor name search

__ikm_find_monitor_name() relies on strstr() to find a monitor by name,
which fails if the target monitor is a substring of a previously listed
monitor.

Fix it by tokenizing the available_monitors file and matching full
tokens instead.

Fixes: eba321a16fc6 ("tools/rv: Add support for nested monitors")
Reviewed-by: Nam Cao <namcao@linutronix.de>
Link: https://lore.kernel.org/r/20260514152055.229162-2-gmonaco@redhat.com
Signed-off-by: Gabriele Monaco <gmonaco@redhat.com>