drm/amdgpu/vcn: include header for vcn_dec_sw_ring_emit_fence

Fixed warning: no previous prototype for 'vcn_dec_sw_ring_emit_fence'.

v2: regenerate patch after git rebase.
v3: update commit message.
Signed-off-by: James Zhu <James.Zhu@amd.com>
Reported-by: kernel test robot <lkp@intel.com>
Reviewed-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

drivers/gpu/drm/amd/amdgpu/vcn_sw_ring.c

@@ -22,6 +22,7 @@
  */
 
 #include "amdgpu.h"
+#include "vcn_sw_ring.h"
 
 void vcn_dec_sw_ring_emit_fence(struct amdgpu_ring *ring, u64 addr,
 	u64 seq, uint32_t flags)