libxc: simplify HYPERCALL_BUFFER()

libxc: simplify HYPERCALL_BUFFER()

_hcbuf_buf1 has been there only for a pointer comparison to validate
type compatibility. The same can be achieved by not using typeof() on
the definition of what so far was _hcbuf_buf2, as the initializer has
to also be type-compatible. Drop _hcbuf_buf1 and the comaprison;
rename _hcbuf_buf2.

Since we're already using compiler extensions here, don't be shy and
also omit the middle operand of the involved ?: operator.

Bring line continuation character placement in line with that of
related macros.

Signed-off-by: Jan Beulich <jbeulich@suse.com>
Acked-by: Andrew Cooper <andrew.cooper3@citrix.com>