mm: kfence: fix false positives on big endian

Since commit 1ba3cbf3 ("mm: kfence: improve the performance of
__kfence_alloc() and __kfence_free()"), kfence reports failures in random
places at boot on big endian machines.

The problem is that the new KFENCE_CANARY_PATTERN_U64 encodes the address
of each byte in its value, so it needs to be byte swapped on big endian
machines.

The compiler is smart enough to do the le64_to_cpu() at compile time, so
there is no runtime overhead.

Link: https://lkml.kernel.org/r/20230505035127.195387-1-mpe@ellerman.id.au
Fixes: 1ba3cbf3

 ("mm: kfence: improve the performance of __kfence_alloc() and __kfence_free()")
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Reviewed-by: Alexander Potapenko <glider@google.com>
Reviewed-by: Marco Elver <elver@google.com>
Cc: Peng Zhang <zhangpeng.00@bytedance.com>
Cc: David Laight <David.Laight@ACULAB.COM>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>