PCI: imx6: Improve comment for workaround ERR010728

Improve comment about workaround ERR010728 by using official errata
document content, see:

  https://www.nxp.com/webapp/Download?colCode=IMX7DS_2N09P

Link: https://lore.kernel.org/linux-pci/20240729-pci2_upstream-v8-7-b68ee5ef2b4d@nxp.com


Signed-off-by: Frank Li <Frank.Li@nxp.com>
[kwilczynski: commit log]
Signed-off-by: Krzysztof Wilczyński <kwilczynski@kernel.org>
Reviewed-by: Manivannan Sadhasivam <manivannan.sadhasivam@linaro.org>