Replace the open-coded implementation for reading the PCIe DSN with
pci_get_dsn().

Use of put_unaligned_le64 should be correct. pci_get_dsn() will perform
two pci_read_config_dword calls. The first dword will be placed in the
first 32 bits of the u64, while the second dword will be placed in the
upper 32 bits of the u64.

On Little Endian systems, the least significant byte comes first, which
will be the least significant byte of the first dword, followed by the
least significant byte of the second dword. Since the _le32 variations
do not perform byte swapping, we will correctly copy the dwords into the
dsn[] array in the same order as before.

On Big Endian systems, the most significant byte of the second dword
will come first. put_unaligned_le64 will perform a CPU_TO_LE64, which
will swap things correctly before copying. This should also end up with
the correct bytes in the dsn[] array.

While at it, fix a small typo in the netdev_info error message when the
DSN cannot be read.
Signed-off-by: Jacob Keller <jacob.e.keller@intel.com>
Cc: Michael Chan <michael.chan@broadcom.com>
Signed-off-by: David S. Miller <davem@davemloft.net>