[PIC16 LIB] Improve clock driver
[PIC16 LIB] Improve clock driver

- Add delay after clock switch to wait target clock source stable.

Signed-off-by: Wang Ge <93a3a7c61d46cf8efe5c7ab1fdc8a5d1e4c57769@freescale.com>

JimmyWang1989/EventQueueX