drm/amd/display: use FB pitch to fill dc_cursor_attributes

Instead of relying on pitch (in pixels) == width, use the FB pitch. This
is less confusing to readers, and works correctly if we ever support FBs
with a pitch (in pixels) != width.

This also makes the code symmetrical with fill_plane_buffer_attributes.

Reviewed-by: Nicholas Kazlauskas <nicholas.kazlauskas@amd.com>
Signed-off-by: Simon Ser <contact@emersion.fr>
Cc: Alex Deucher <alexander.deucher@amd.com>
Cc: Harry Wentland <hwentlan@amd.com>
Cc: Nicholas Kazlauskas <nicholas.kazlauskas@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>