Fix a bug introduced in r223938; on big-endian machines coping a 32-bit
quantum bytewise to the address of a 64-bit variable results in writing
to the "wrong" 32-bit half so adjust the address accordingly. This fix
is implemented in a hackish way for two reasons:
o in order to be able to get it into 8.3 with zero impact on the little-

endian architectures where this bug has no effect and

o to avoid blowing the x86 boot2 out of the water again when compiling

it with clang, which all sane versions of this fix tested do.

This change fixes booting from UFS1 file systems on big-endian machines.

MFC after: 3 days