drm/i915: Fix broken num_entries in skl_ddb_allocation_overlaps

skl_ddb_allocation_overlaps() num_entries hass been passed as
INTEL_NUM_PIPES, it should be I915_MAX_PIPES.

v2:
- Rebased.

Cc: Ville Syrjälä <ville.syrjala@linux.intel.com>
Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Signed-off-by: Anshuman Gupta <anshuman.gupta@intel.com>
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20200224124004.26712-8-anshuman.gupta@intel.com