rf230bb: Use radio_is_sleeping to judge the state of RF

Signed-off-by Zhong Hongbo <bocui107@163.com>
rf230bb: Fix double checked the state of SPL_TR

Since rf230_isidle checked the state of SPL_TR, So
it is not necessary to checke it's state again.

Signed-off-by Zhong Hongbo <bocui107@163.com>