Function mvebu_pcie_hw_rd_conf() does not handle invalid size. So correctly
set read value to all-ones and return appropriate error return value
PCIBIOS_BAD_REGISTER_NUMBER like in mvebu_pcie_hw_wr_conf() function.

Link: https://lore.kernel.org/r/20211125124605.25915-5-pali@kernel.orgSigned-off-by: NPali Rohár <pali@kernel.org>
Signed-off-by: NLorenzo Pieralisi <lorenzo.pieralisi@arm.com>