PCI/DOE: Fix maximum data object length miscalculation

PCI/DOE: Fix maximum data object length miscalculation

commit a4ff8e7a71601321f7bf7b58ede664dc0d774274 upstream.

Per PCIe r6.0, sec 6.30.1, a data object Length of 0x0 indicates 2^18
DWORDs (256K DW or 1MB) being transferred.  Adjust the value of data object
length for this case on both sending side and receiving side.

Don't bother checking whether Length is greater than SZ_1M because all
values of the 18-bit Length field are valid, and it is impossible to
represent anything larger than SZ_1M:

  0x00000    256K DW (1M bytes)
  0x00001       1 DW (4 bytes)
  ...
  0x3ffff  256K-1 DW (1M - 4 bytes)

[bhelgaas: commit log]
Link: https://lore.kernel.org/r/20221116015637.3299664-1-ming4.li@intel.com
Fixes: 48d4347be462 ("PCI/DOE: Add DOE mailbox support functions")
Signed-off-by: Li Ming <ming4.li@intel.com>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Reviewed-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
Reviewed-by: Lukas Wunner <lukas@wunner.de>
Cc: stable@vger.kernel.org	# v6.0+
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>