ring_buffer: Fix return types
ring_buffer: Fix return types

Fixed return types for capacity and space get functions.
Prevents potential overflows.

Signed-off-by: Tomás Longeri <4701108e701bf60d6548ceabf676a1260c86f065@gmail.com>

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