PCI: keystone: Fix link training retries initiation

ks_pcie_stop_link() function does not clear LTSSM_EN_VAL bit so
link training was not triggered more than once after startup.
In configurations where link can be unstable during early boot,
for example, under low temperature, it will never be established.

Fixes: 0c4ffcfe ("PCI: keystone: Add TI Keystone PCIe driver")
Signed-off-by: Yurii Monakov <monakov.y@gmail.com>
Signed-off-by: Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>
Acked-by: Andrew Murray <andrew.murray@arm.com>
Cc: stable@vger.kernel.org

drivers/pci/controller/dwc/pci-keystone.c

@@ -510,7 +510,7 @@ static void ks_pcie_stop_link(struct dw_pcie *pci)
 	/* Disable Link training */
 	val = ks_pcie_app_readl(ks_pcie, CMD_STATUS);
 	val &= ~LTSSM_EN_VAL;
-	ks_pcie_app_writel(ks_pcie, CMD_STATUS, LTSSM_EN_VAL | val);
+	ks_pcie_app_writel(ks_pcie, CMD_STATUS, val);
 }
 
 static int ks_pcie_start_link(struct dw_pcie *pci)