tools: tests: remove dependency on grep

tools: tests: remove dependency on grep

We only use grep in one place where we don't really need it as we can use
find directly.

Reported-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Suggested-by: Kent Gibson <warthog618@gmail.com>
Reviewed-by: Kent Gibson <warthog618@gmail.com>
Reviewed-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Link: https://lore.kernel.org/r/20240528-fix-bash-tests-v3-4-e9b5be2ba8bf@linaro.org
Signed-off-by: Bartosz Golaszewski <bartosz.golaszewski@linaro.org>