kernel: pipes: fix build warnings
kernel: pipes: fix build warnings

Resolves void pointer arithmetic build warnings in k_pipe_put() by
casting the pointer to a uint8_t pointer.

Signed-off-by: Peter Mitsis <22bf95476f8cdbda3c8a9a9bf1bdda876f69ea7a@intel.com>

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