dshot: reduce static buffer size

And handle failures of up_dshot_init().

On Omnibus: reduces memory usage if dshot is enabled by ~1.0KB.
The buffer is roughly 1KB in size.

boards/px4/fmu-v5x/src/board_config.h

@@ -672,6 +672,8 @@
 
 #define BOARD_ENABLE_CONSOLE_BUFFER
 
+#define BOARD_NUM_IO_TIMERS 5
+
 __BEGIN_DECLS
 
 /****************************************************************************************************