drm/i915: Initialize the mbus_offset to fix Klockwork issue

Static analysis identified an issue in skl_crtc_allocate_ddb where
mbus_offset may be used uninitialized.
This patch fixes it.

Fixes: 835c176c ("drm/i915: Introduce MBUS relative dbuf offsets")
Cc: Ville Syrjälä <ville.syrjala@linux.intel.com>
Signed-off-by: NManasi Navare <manasi.d.navare@intel.com>
Signed-off-by: NJani Nikula <jani.nikula@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20210603215338.13804-1-manasi.d.navare@intel.com

drivers/gpu/drm/i915/intel_pm.c

@@ -4163,7 +4163,7 @@ skl_crtc_allocate_ddb(struct intel_atomic_state *state, struct intel_crtc *crtc)
 	struct intel_crtc_state *crtc_state;
 	struct skl_ddb_entry ddb_slices;
 	enum pipe pipe = crtc->pipe;
-	unsigned int mbus_offset;
+	unsigned int mbus_offset = 0;
 	u32 ddb_range_size;
 	u32 dbuf_slice_mask;
 	u32 start, end;