drm/amd/pp: initialize result to before or'ing in data

The current use of result is or'ing in values and checking for
a non-zero result, however, result is not initialized to zero
so it potentially contains garbage to start with. Fix this by
initializing it to the first return from the call to
vega10_program_didt_config_registers.

Detected by cppcheck:
"(error) Uninitialized variable: result"

Fixes: 9b7b8154 ("drm/amd/powerplay: added didt support for vega10")
Signed-off-by: Colin Ian King <colin.king@canonical.com>
Acked-by: Huang Rui <ray.huang@amd.com>
[Fix the subject as Colin's comment]
Signed-off-by: Huang Rui <ray.huang@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
Cc: stable@vger.kernel.org