drm/amd/display: fix transfer function passed to build_coefficients()

The default argument should be enum TRANSFER_FUNCTION_SRGB rather than
the current boolean value which improperly maps to
TRANSFER_FUNCTION_BT709.

Commit 9b3d7652 ("drm/amd/display: Revert adding degamma coefficients")
looks to have improperly reverted
commit d0209709 ("drm/amd/display: Add regamma/degamma coefficients and set sRGB when TF is BT709")
replacing the enum value with a boolean value.

Cc: Krunoslav Kovac <Krunoslav.Kovac@amd.com>
Cc: Jaehyun Chung <jaehyun.chung@amd.com>
Cc: Zeng Heng <zengheng4@huawei.com>
Fixes: 9b3d7652

 ("drm/amd/display: Revert adding degamma coefficients")
Reviewed-by: Harry Wentland <harry.wentland@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>