libxc: Fix do_memory_op to return negative value on errors

libxc: Fix do_memory_op to return negative value on errors

instead of the -Exx values (which should go in errno).

This patch has HUGE implications. There is a lot of APIs
that are using do_memory_op. Fortunately most of them
check for 'if (do_memory_op(..) < 0)' so will function
properly. However there were some which printed the return
value to the user. They have been fixed in:

 libxc: Don't assign return value to errno for E820 get/set xc_ calls.
 libxc: Check xc_sharing_* for proper return values.
 libxc: If xc_domain_add_to_physmap fails, include errno value
 libxc: Check xc_maximum_ram_page for negative return values.
 libxc: Check xc_domain_maximum_gpfn for negative return values

Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
Acked-by: Ian Campbell <ian.campbell@citrix.com>