efi/cper: Fix endianness of PCIe class code

The CPER parser assumes that the class code is big endian, but at least
on this edk2-derived Intel Purley platform it's little endian:

    efi: EFI v2.50 by EDK II BIOS ID:PLYDCRB1.86B.0119.R05.1701181843
    DMI: Intel Corporation PURLEY/PURLEY, BIOS PLYDCRB1.86B.0119.R05.1701181843 01/18/2017

    {1}[Hardware Error]:   device_id: 0000:5d:00.0
    {1}[Hardware Error]:   slot: 0
    {1}[Hardware Error]:   secondary_bus: 0x5e
    {1}[Hardware Error]:   vendor_id: 0x8086, device_id: 0x2030
    {1}[Hardware Error]:   class_code: 000406
                                       ^^^^^^ (should be 060400)

Signed-off-by: Lukas Wunner <lukas@wunner.de>
Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Cc: Ben Dooks <ben.dooks@codethink.co.uk>
Cc: Dave Young <dyoung@redhat.com>
Cc: Jarkko Sakkinen <jarkko.sakkinen@linux.intel.com>
Cc: Jerry Snitselaar <jsnitsel@redhat.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Lyude Paul <lyude@redhat.com>
Cc: Matthew Garrett <mjg59@google.com>
Cc: Octavian Purdila <octavian.purdila@intel.com>
Cc: Peter Jones <pjones@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Scott Talbert <swt@techie.net>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: linux-efi@vger.kernel.org
Cc: linux-integrity@vger.kernel.org
Link: https://lkml.kernel.org/r/20191002165904.8819-2-ard.biesheuvel@linaro.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>

drivers/firmware/efi/cper.c

@@ -381,7 +381,7 @@ static void cper_print_pcie(const char *pfx, const struct cper_sec_pcie *pcie,
 		printk("%s""vendor_id: 0x%04x, device_id: 0x%04x\n", pfx,
 		       pcie->device_id.vendor_id, pcie->device_id.device_id);
 		p = pcie->device_id.class_code;
-		printk("%s""class_code: %02x%02x%02x\n", pfx, p[0], p[1], p[2]);
+		printk("%s""class_code: %02x%02x%02x\n", pfx, p[2], p[1], p[0]);
 	}
 	if (pcie->validation_bits & CPER_PCIE_VALID_SERIAL_NUMBER)
 		printk("%s""serial number: 0x%04x, 0x%04x\n", pfx,