resource: Use getter/setter of struct resource for encapsulation

resource: Use getter/setter of struct resource for encapsulation

Prevent the direct access of the fields of struct resource
by using getter/setter functiosn of struct resource.

By this change, keep the encapsulation of struct resource
and only communicate via getter/setter functions.

Change-Id: I4c7b92b79197ef67688773a5ef6b7db5e044bc09
Signed-off-by: Chanwoo Choi <cw00.choi@samsung.com>