drm/amdgpu: make wait_event uninterruptible in push_job

with interruptible, the push_job maybe return -ERESTARTSYS,
then result in push_job error.

E.g. bug trace:
[  181.618860] *****amdgpu_copy_buffer:fence->seq:0x0000000048d8758b, contxt:1207959552, ref:683967304, r:-512
[  181.618929] BUG: unable to handle kernel paging request at ffffffff811aa266
[  181.625887] IP: [<ffffffff81548ffc>] reservation_object_add_excl_fence+0x3c/0x120
...
[  181.859767]  [<ffffffff811aa266>] ? unmap_mapping_range+0x66/0x110
[  181.865928]  [<ffffffffc0608ac1>] ttm_bo_move_accel_cleanup+0x41/0x3c0 [ttm]
[  181.872971]  [<ffffffffc062d382>] amdgpu_move_blit.isra.18+0x122/0x150 [amdgpu]
[  181.880254]  [<ffffffff811aa266>] ? unmap_mapping_range+0x66/0x110
[  181.886420]  [<ffffffffc062d709>] amdgpu_bo_move+0xa9/0x200 [amdgpu]
[  181.892753]  [<ffffffffc0606e8d>] ttm_bo_handle_move_mem+0x26d/0x5c0 [ttm]

Signed-off-by: Chunming Zhou <david1.zhou@amd.com>
Reviewed-by: Christian König <christian.koenig@amd.com>