lib/crypto: powerpc/aes: Fix rndkey_from_vsx() on big endian CPUs

lib/crypto: powerpc/aes: Fix rndkey_from_vsx() on big endian CPUs

I finally got a big endian PPC64 kernel to boot in QEMU.  The PPC64 VSX
optimized AES library code does work in that case, with the exception of
rndkey_from_vsx() which doesn't take into account that the order in
which the VSX code stores the round key words depends on the endianness.
So fix rndkey_from_vsx() to do the right thing on big endian CPUs.

Fixes: 7cf2082e74ce ("lib/crypto: powerpc/aes: Migrate POWER8 optimized code into library")
Link: https://lore.kernel.org/r/20260216022104.332991-1-ebiggers@kernel.org
Signed-off-by: Eric Biggers <ebiggers@kernel.org>