sparc: Most unaligned_64.c tweaks for branch tracer warnings.

arch/sparc/kernel/unaligned_64.c: In function 'handle_lddfmna':
arch/sparc/kernel/unaligned_64.c:592: warning: 'second' may be used uninitialized in this function

Signed-off-by: David S. Miller <davem@davemloft.net>