drm/amdgpu: drop unexpected word 'for' in comments

there is an unexpected word 'for' in the comments that need to be dropped

file - drivers/gpu/drm/amd/amdgpu/amdgpu_ih.c
line - 245

 * position and also advance the position for for Vega10

changed to:

 * position and also advance the position for Vega10

Signed-off-by: Jiang Jian <jiangjian@cdjrlc.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>