PCI: exynos: Rename all pointer names from "exynos_pcie" to "ep"

Rename the simple pointer name as "ep" instead of "exynos_pcie".  After
applying this patch, it can save the 10 characthers within one line.
Signed-off-by: Jaehoon Chung <jh80.chung@samsung.com>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Reviewed-by: Pankaj Dubey <pankaj.dubey@samsung.com>
Acked-by: Krzysztof Kozlowski <krzk@kernel.org>
Acked-by: Jingoo Han <jingoohan1@gmail.com>