samples: modules: lvgl: demos: Increase memory pool on native

Due to the added overhead on 64 bit native, we also need to increase
the memory pool size to fix crashes as described in here:

lvgl/lvgl#7648

Signed-off-by: Detlev Zundel <[email protected]>

Author: laodzu

samples/modules/lvgl/demos/boards/native_sim_native_64.conf

@@ -2,4 +2,4 @@
 # SPDX-License-Identifier: Apache-2.0
 
 CONFIG_LV_COLOR_DEPTH_32=y
-CONFIG_LV_Z_MEM_POOL_SIZE=75264
+CONFIG_LV_Z_MEM_POOL_SIZE=81920