drm/i915: Fix fractional bpp handling in intel_link_bw_reduce_bpp()

drm/i915: Fix fractional bpp handling in intel_link_bw_reduce_bpp()

Convert crtc_state->pipe_bpp to U6.4 format as expected by the rest of
the function.

Fixes: 59a266f068b4 ("drm/i915/display: Store compressed bpp in U6.4 format")
Cc: Ankit Nautiyal <ankit.k.nautiyal@intel.com>
Cc: Suraj Kandpal <suraj.kandpal@intel.com>
Cc: Sui Jingfeng <suijingfeng@loongson.cn>
Reviewed-by: Ankit Nautiyal <ankit.k.nautiyal@intel.com>
Signed-off-by: Imre Deak <imre.deak@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20231114141012.603960-1-imre.deak@intel.com