tools/libxc: Correct read_exact() error messages

The errors have been incorrectly identifying their function since c/s
861aef6e15 which did a lot of error handling
cleanup.

Use __func__ to ensure the name remains correct in the future.

Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com>
Acked-by: Ian Campbell <Ian.Campbell@citrix.com>
CC: Ian Jackson <Ian.Jackson@eu.citrix.com>

tools/libxc/xc_domain_restore.c

@@ -87,7 +87,7 @@ static ssize_t rdexact(xc_interface *xch, struct restore_ctx *ctx,
             if ( len == -1 && errno == EINTR )
                 continue;
             if ( !FD_ISSET(fd, &rfds) ) {
-                ERROR("read_exact_timed failed (select returned %zd)", len);
+                ERROR("%s failed (select returned %zd)", __func__, len);
                 errno = ETIMEDOUT;
                 return -1;
             }
@@ -101,7 +101,7 @@ static ssize_t rdexact(xc_interface *xch, struct restore_ctx *ctx,
             errno = 0;
         }
         if ( len <= 0 ) {
-            ERROR("read_exact_timed failed (read rc: %d, errno: %d)", len, errno);
+            ERROR("%s failed (read rc: %d, errno: %d)", __func__, len, errno);
             return -1;
         }
         offset += len;