drm/i915/bw: Fix 'deinterleave' rounding direction

drm/i915/bw: Fix 'deinterleave' rounding direction

For some reason we're rounding up when calculating the deinterleave
value. But the spec says we should round down. Fix it.

But I suppose this doesn't actually matter since the deinterleave
values should always be power of two. The only exception is therefore
the deinterleave==1 case, which gets handled by the max(..., 1).

Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patch.msgid.link/20260522200346.17377-5-ville.syrjala@linux.intel.com
Reviewed-by: Michał Grzelak <michal.grzelak@intel.com>