device: restore init_res bit field

After b5f3cf8 some platforms
(qemu_riscv32_xip) are not able to boot. Re-introduce the bit field for
init_res, using `unsigned int` (valids are signed/unsigned int, and
bool).

Signed-off-by: Gerard Marull-Paretas <[email protected]>

Author: gmarull

include/zephyr/device.h

@@ -354,9 +354,9 @@ struct device_state {
 	 *
 	 * Device initialization functions return a negative errno code if they
 	 * fail. In Zephyr, errno values do not exceed 255, so we can store the
-	 * positive result value in a uint8_t type.
+	 * positive result value using 8 bits.
 	 */
-	uint8_t init_res;
+	unsigned int init_res : 8;
 
 	/** Indicates the device initialization function has been
 	 * invoked.