Make supportive_resolution initial.

Make supportive_resolution initial.

After applying this patch, 'supportive_resolution' has initial value when call 'scmirroring_sink_unprepare'.
Now, 'supportive_resolution' can be set initial value after calling 'scmirroring_sink_unprepare' even though user set user preferred value when using.
*Before, once 'supportive_resolution' is set through 'scmirorring_set_resolution' api, 'supportive_resolution' variable couldn't be set initial value before screen mirroring app is terminated.
Signed-off-by: Hyunsoo <hance.park@samsung.com>
Change-Id: I855e79f304b8aec0ec904343844320a1903956a3