console: Fix unreachable code condition

This patch fixes an unreachable code condition in the uart_console
driver.

If UART_CONSOLE_DEBUG_SERVER_HOOKS was not defined
handled_by_debug_server in console_out was always 0.

This issue was reported by Coverity (CID 131627).

Change-Id: I4376c3e5b3e68220218df6aabd91b6a8900ca31f
Signed-off-by: Vincenzo Frascino <vincenzo.frascino@linaro.org>