drm/amd/powerplay: fix amd_powerplay_reset()

We accidentally inverted an if statement and turned amd_powerplay_reset()
into a no-op.

Fixes: ae97988f ("drm/amd/powerplay: tidy up ret checks in amd_powerplay.c (v3)")
Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>