libxc: mmapbatch-v2 adjustments

libxc: mmapbatch-v2 adjustments

Just like the kernel, the fallback implementation of
xc_map_foreign_bulk() should clear the error indication array upon
success.

Also, a few allocations were needlessly using calloc() instead of
malloc().

Finally, in xc_domain_save() allocate the error indicator array once
(along with the other arrays) instead of using realloc() (without
error checking) in the loop body.

Signed-off-by: Jan Beulich <jbeulich@novell.com>