drm/amdgpu: delete duplicate condition in gfx_v11_0_soft_reset()

We know that "grbm_soft_reset" is true because we're already inside an
if (grbm_soft_reset) condition.  No need to test again.

Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>