kernel: mmu: Fix access to unpacked member inside packed struct
kernel: mmu: Fix access to unpacked member inside packed struct

The following warning is triggered by GCC when
-Waddress-of-packed-member is enabled:

/home/carles/src/zephyr/zephyr/kernel/mmu.c: In function
'free_page_frame_list_put':
/home/carles/src/zephyr/zephyr/kernel/mmu.c:383:42: warning: taking
address of packed member of 'struct z_page_frame' may result in an
unaligned pointer value [-Waddress-of-packed-member]
  383 |  sys_slist_append(&free_page_frame_list, &pf->node);

This is due to the fact that sys_snode_t node is an unpacked structure
inside a packed z_page_frame structure, so that the alignment of the
former cannot be ensured if placed inside the latter.

Given that alignment of z_page_frame is ensured by the code, silence the
compiler by going through an intermediate variable.

More info in #16587.

Signed-off-by: Carles Cufi <853081dc8dca4fe6a7e3c984752718b5db36e060@nordicsemi.no>

galak/zephyr,finikorg/zephyr,finikorg/zephyr,finikorg/zephyr,finikorg/zephyr,zephyrproject-rtos/zephyr,zephyrproject-rtos/zephyr,galak/zephyr,galak/zephyr,galak/zephyr,finikorg/zephyr,zephyrproject-rtos/zephyr,galak/zephyr,zephyrproject-rtos/zephyr,zephyrproject-rtos/zephyr