PCI: dw-rockchip: Simplify regulator setup with devm_regulator_get_enable_optional()

PCI: dw-rockchip: Simplify regulator setup with devm_regulator_get_enable_optional()

Replace manual get/enable logic with devm_regulator_get_enable_optional()
to reduce boilerplate and improve error handling. This devm helper ensures
the regulator is enabled during probe and automatically disabled when the
platform device is freed.

Also drop the redundant 'rockchip_pcie::vpcie3v3' pointer.

Signed-off-by: Anand Moon <linux.amoon@gmail.com>
Signed-off-by: Manivannan Sadhasivam <mani@kernel.org>
Link: https://patch.msgid.link/20250905112736.6401-1-linux.amoon@gmail.com