[nrf noup] settings: performance: fix storage size

When partition manager tries to assign the partition size for the
settings it allocates the minimum size which is 8K bytes.
This is not enough for the performance test.
Change it to 32K bytes.

Signed-off-by: Riadh Ghaddab <[email protected]>

Author: rghaddab

tests/subsys/settings/performance/prj.conf

@@ -5,3 +5,5 @@ CONFIG_ZMS=y
 
 CONFIG_SETTINGS=y
 CONFIG_SETTINGS_RUNTIME=y
+
+CONFIG_PM_PARTITION_SIZE_SETTINGS_STORAGE=0x8000