drm/amd/display: Remove redundant ternary operation

[WHY]
Coverity analysis flagged this ternary operation as
DEADCODE.

Since 'total_y_free_entry' is initialized as 0x200 and
'total_c_free_entry' is initialized as 0x140, and they
never change values before the ternary operator, so
'total_y_free_entry' is always greater 'total_c_free_entry',
'so small_free_entry' is always set to 'total_c_free_entry'.

[HOW]
Replace the ternary operator with the variable declaration.

Signed-off-by: Ivan Lipski <ivlipski@amd.com>
Acked-by: Zaeem Mohamed <zaeem.mohamed@amd.com>
Tested-by: Daniel Wheeler <daniel.wheeler@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>