tests/settings/nvs: Specify TFM maximum asset size

When using the TFM version of trusted storage, we need
to specify the maximum asset size.

Signed-off-by: Keith Packard <keithp@keithp.com>

Author: keith-packard

tests/subsys/settings/nvs/prj.conf

@@ -6,3 +6,6 @@ CONFIG_NVS=y
 CONFIG_SETTINGS=y
 CONFIG_SETTINGS_RUNTIME=y
 CONFIG_SETTINGS_NVS=y
+
+CONFIG_TFM_ITS_MAX_ASSET_SIZE_OVERRIDE=y
+CONFIG_TFM_ITS_MAX_ASSET_SIZE=256