Newer DSI host controllers (SDM845 in particular) require a new clock
called byte_intf_clk. A recent patch tried to add this as an optional
clock, but it still set 'ret' to an error number if it didn't find it.
This breaks the host's probe for all previous DSI host versions.

Instead of setting this up as an optional clock, try to get the clock
only for the DSI version that supports it.

Fixes: 56558fb ("drm/msm/dsi: Add byte_intf_clk")
Signed-off-by: Archit Taneja <architt@codeaurora.org>
Signed-off-by: Rob Clark <robdclark@gmail.com>