[api] using "unit" key to get the dimension for fc layer

[api] using "unit" key to get the dimension for fc layer

Instead of using input_shape to get the fc layer dimenson, it is
simple to get the ouptut dimesion using unit keyword.

**Self evaluation:**
1. Build test:	 [X]Passed [ ]Failed [ ]Skipped
2. Run test:	 [X]Passed [ ]Failed [ ]Skipped

Signed-off-by: jijoong.moon <jijoong.moon@samsung.com>