PCI: qcom-ep: Switch MHI bus master clock off during L1SS

Currently, as part of the qcom_pcie_perst_deassert() function, instead
of writing the updated value to clear PARF_MSTR_AXI_CLK_EN, the variable
"val" is re-read.

This must be fixed to ensure that the master clock supplied to the MHI
bus is correctly gated during L1.1/L1.2 to save power.

Thus, replace the line that re-reads "val" with a line that writes the
updated value to the register to clear PARF_MSTR_AXI_CLK_EN.

[kwilczynski: commit log]
Fixes: c457ac0 ("PCI: qcom-ep: Gate Master AXI clock to MHI bus during L1SS")
Link: https://lore.kernel.org/linux-pci/20230627141036.11600-1-manivannan.sadhasivam@linaro.org
Reported-by: Krzysztof Wilczyński <kwilczynski@kernel.org>
Signed-off-by: Manivannan Sadhasivam <manivannan.sadhasivam@linaro.org>
Signed-off-by: Krzysztof Wilczyński <kwilczynski@kernel.org>

Author: Mani-Sadhasivam

drivers/pci/controller/dwc/pcie-qcom-ep.c

@@ -415,7 +415,7 @@ static int qcom_pcie_perst_deassert(struct dw_pcie *pci)
 	/* Gate Master AXI clock to MHI bus during L1SS */
 	val = readl_relaxed(pcie_ep->parf + PARF_MHI_CLOCK_RESET_CTRL);
 	val &= ~PARF_MSTR_AXI_CLK_EN;
-	val = readl_relaxed(pcie_ep->parf + PARF_MHI_CLOCK_RESET_CTRL);
+	writel_relaxed(val, pcie_ep->parf + PARF_MHI_CLOCK_RESET_CTRL);
 
 	dw_pcie_ep_init_notify(&pcie_ep->pci.ep);