accel: Avoid aggregate initialization for C struct.

When a union is initialized by aggregate initialization, only its
first non-static data member is initialized. So if a C struct
contains union data members, other data members are not initialized.

This CL replaces aggregate initialization of all v4l2 related struct
with memset(), to ensure the struct is initialized correctly.

Bug: 153935975
Test: mmm external/v4l2_codec2

Change-Id: I11550e1ebcce3a69e5f0ccd814f6413f7ce8aabf
1 file changed