drm/amd/display: Fix negative cursor pos programming

drm/amd/display: Fix negative cursor pos programming

[Why]
If the cursor pos passed from DM is less than the plane_state->dst_rect
top left corner then the unsigned cursor pos wraps around to a large
positive number since cursor pos is a u32.

There was an attempt to guard against this in hubp1_cursor_set_position
by checking the src_x_offset and src_y_offset and offseting the
cursor hotspot within hubp1_cursor_set_position.

However, the cursor position itself is still being programmed
incorrectly as a large value.

This manifests itself visually as the cursor disappearing or containing
strange artifacts near the middle of the screen on raven.

[How]
Don't subtract the destination rect top left corner from the pos but
add it to the hotspot instead. This happens before the pos gets
passed into hubp1_cursor_set_position.

This achieves the same result but avoids the subtraction wrap around.
With this fix the original cursor programming logic can be used again.

Signed-off-by: Nicholas Kazlauskas <nicholas.kazlauskas@amd.com>
Reviewed-by: Charlene Liu <Charlene.Liu@amd.com>
Acked-by: Leo Li <sunpeng.li@amd.com>
Acked-by: Murton Liu <Murton.Liu@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>