drm/amd/display: Remove duplicate/repeating expression

Remove duplicate or repeating expressions in the if condition
evaluation. Issue identified using doubletest.cocci Coccinelle semantic
patch.

Reviewed-by: Harry Wentland <harry.wentland@amd.com>
Signed-off-by: Deepak R Varma <drv@mailo.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>