drm/amdgpu: Fix JPEG v4.0.3 register write

EXTERNAL_REG_INTERNAL_OFFSET/EXTERNAL_REG_WRITE_ADDR should be used in
pairs. If an external register shouldn't be written, both packets
shouldn't be sent.

Fixes: a78b4814 ("drm/amdgpu: Skip PCTL0_MMHUB_DEEPSLEEP_IB write in jpegv4.0.3 under SRIOV")
Signed-off-by: Lijo Lazar <lijo.lazar@amd.com>
Acked-by: Leo Liu <leo.liu@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>