drm/amd/display: fixed that I2C over AUX didn't read data issue

[Why]
The variable mismatch assignment error.

[How]
To use uint32_t replace it.

Signed-off-by: Brandon Syu <Brandon.Syu@amd.com>
Reviewed-by: Charlene Liu <Charlene.Liu@amd.com>
Acked-by: Leo Li <sunpeng.li@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>