zephyr: hooks test: bump DEFERRED_DELAY_US
zephyr: hooks test: bump DEFERRED_DELAY_US

Apparently 250ms is too sensitive for Zephyr v2.6 and the test fails:

*** Booting Zephyr OS build zephyr-v2.6.0-77-g656dcdda8d73  ***
Running test suite hooks_tests
===================================================================
START - test_hook_list_multiple
 PASS - test_hook_list_multiple in 0.0 seconds
===================================================================
START - test_hook_list_single
 PASS - test_hook_list_single in 0.0 seconds
===================================================================
START - test_hook_list_empty
 PASS - test_hook_list_empty in 0.0 seconds
===================================================================
START - test_deferred_func
 PASS - test_deferred_func in 0.510 seconds
===================================================================
START - test_deferred_func_push_out

    Assertion failed at CMAKE_SOURCE_DIR/hooks.c:116:
    test_deferred_func_push_out: (deferred_func_2_called is true)
The deferred function was called, but should not have been
 FAIL - test_deferred_func_push_out in 0.510 seconds
===================================================================
START - test_deferred_func_cancel
 PASS - test_deferred_func_cancel in 0.510 seconds
===================================================================
Test suite hooks_tests failed.
===================================================================
PROJECT EXECUTION FAILED

Bump to 500ms so we can support Zephyr v2.6.

BUG=b:195571108
BRANCH=none
TEST=passes on both v2.5 and v2.6

Signed-off-by: Jack Rosenthal <d3f605bef1867f59845d4ce6e4f83b8dc9e4e0ae@chromium.org>
Change-Id: Id090fe9e678c9f168e3a1c3f90f048089a638fff
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/platform/ec/+/3072416
Commit-Queue: Fabio Baltieri <1c55e39c05d9ab42261288cf330256b2af6ba179@google.com>
Reviewed-by: Fabio Baltieri <1c55e39c05d9ab42261288cf330256b2af6ba179@google.com>

coreboot/chrome-ec,coreboot/chrome-ec,coreboot/chrome-ec,coreboot/chrome-ec,coreboot/chrome-ec,coreboot/chrome-ec