libxc: Fix misleading use of strncpy code in build_hvm_info()

libxc: Fix misleading use of strncpy code in build_hvm_info()

hvm_info->signature is not a string, but an 64 bit int, and is not
NULL terminated.  The use of strncpy to populate it is inappropriate and
potentially misleading.  A cursory glance might have you thinking someone
had miscounted the length of the string literal - not realising it was
intentionally cropping of the null termination.
Also, since we wish to initialise all of hvm_info->signature, and
certainly no more, the use of sizeof is safer.

Coverity-ID: 1198710

Signed-off-by: Jennifer Herbert <jennifer.herbert@citrix.com>
Reviewed-by: Andrew Cooper <andrew.cooper3@citrix.com>
Acked-by: Ian Campbell <ian.campbell@citrix.com>
Acked-by: Ian Jackson <ian.jackson@eu.citrix.com>