drm/i915/display: Ensure that ret is always initialized in icl_combo_phy_verify_state

Clang warns:

drivers/gpu/drm/i915/display/intel_combo_phy.c:268:3: warning: variable
'ret' is uninitialized when used here [-Wuninitialized]
                ret &= check_phy_reg(dev_priv, phy, ICL_PORT_TX_DW8_LN0(phy),
                ^~~
drivers/gpu/drm/i915/display/intel_combo_phy.c:261:10: note: initialize
the variable 'ret' to silence this warning
        bool ret;
                ^
                 = 0
1 warning generated.

In practice, the bug this warning appears to be concerned with would not
actually matter because ret gets initialized to the return value of
cnl_verify_procmon_ref_values. However, that does appear to be a bug
since it means the first hunk of the patch this fixes won't actually do
anything (since the values of check_phy_reg won't factor into the final
ret value). Initialize ret to true then make all of the assignments a
bitwise AND with itself so that the function always does what it should
do.

Fixes: 239bef676d ("drm/i915/display: Implement new combo phy initialization step")
Link: https://github.com/ClangBuiltLinux/linux/issues/1094
Signed-off-by: Nathan Chancellor <natechancellor@gmail.com>
Reviewed-by: Matt Roper <matthew.d.roper@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20200828202830.7165-1-jose.souza@intel.com
Signed-off-by: José Roberto de Souza <jose.souza@intel.com>

drivers/gpu/drm/i915/display/intel_combo_phy.c

@@ -258,7 +258,7 @@ static bool phy_is_master(struct drm_i915_private *dev_priv, enum phy phy)
 static bool icl_combo_phy_verify_state(struct drm_i915_private *dev_priv,
 				       enum phy phy)
 {
-	bool ret;
+	bool ret = true;
 	u32 expected_val = 0;
 
 	if (!icl_combo_phy_enabled(dev_priv, phy))
@@ -276,7 +276,7 @@ static bool icl_combo_phy_verify_state(struct drm_i915_private *dev_priv,
 				     DCC_MODE_SELECT_CONTINUOSLY);
 	}
 
-	ret = cnl_verify_procmon_ref_values(dev_priv, phy);
+	ret &= cnl_verify_procmon_ref_values(dev_priv, phy);
 
 	if (phy_is_master(dev_priv, phy)) {
 		ret &= check_phy_reg(dev_priv, phy, ICL_PORT_COMP_DW8(phy),