Bluetooth: Mesh: Fix heartbeat publication storing
Bluetooth: Mesh: Fix heartbeat publication storing

This fixes usage of an uninitialized variable (to_store) as introduced
by commit bfad2a0.

Fixes #12314

Signed-off-by: Johan Hedberg <628991c7b0a19c384f9b99c21ec330ce952bb838@intel.com>

punitvara/zephyr,ldts/zephyr,punitvara/zephyr,nashif/zephyr,finikorg/zephyr,explora26/zephyr,zephyrproject-rtos/zephyr,punitvara/zephyr,nashif/zephyr,GiulianoFranchetto/zephyr,zephyrproject-rtos/zephyr,Vudentz/zephyr,ldts/zephyr,explora26/zephyr,punitvara/zephyr,finikorg/zephyr,Vudentz/zephyr,zephyrproject-rtos/zephyr,nashif/zephyr,GiulianoFranchetto/zephyr,galak/zephyr,ldts/zephyr,galak/zephyr,GiulianoFranchetto/zephyr,Vudentz/zephyr,explora26/zephyr,zephyrproject-rtos/zephyr,ldts/zephyr,GiulianoFranchetto/zephyr,punitvara/zephyr,finikorg/zephyr,galak/zephyr,nashif/zephyr,GiulianoFranchetto/zephyr,nashif/zephyr,Vudentz/zephyr,galak/zephyr,finikorg/zephyr,Vudentz/zephyr,ldts/zephyr,galak/zephyr,explora26/zephyr,finikorg/zephyr,zephyrproject-rtos/zephyr,Vudentz/zephyr,explora26/zephyr