drm/i915: Fix mbus join config lookup

The bogus loop from compute_dbuf_slices() was copied into
check_mbus_joined() as well. So this lookup is wrong as well.
Fix it.

Cc: stable@vger.kernel.org
Fixes: f4dc0086 ("drm/i915/adl_p: MBUS programming")
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20220207132700.481-2-ville.syrjala@linux.intel.comReviewed-by: Jani Nikula <jani.nikula@intel.com>
(cherry picked from commit 053f2b85)
Signed-off-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>

drivers/gpu/drm/i915/intel_pm.c

@@ -4853,7 +4853,7 @@ static bool check_mbus_joined(u8 active_pipes,
 {
 	int i;
 
-	for (i = 0; i < dbuf_slices[i].active_pipes; i++) {
+	for (i = 0; dbuf_slices[i].active_pipes != 0; i++) {
 		if (dbuf_slices[i].active_pipes == active_pipes)
 			return dbuf_slices[i].join_mbus;
 	}