_cairo_round: Fix documentation

Despite what the comment says, this function rounds halfway cases towards
positive infinity.

_cairo_round ( 0.5) => floor ( 1.0) =>  1.0
_cairo_round (-0.5) => floor ( 0.0) =>  0.0
_cairo_round (-1.5) => floor (-1.0) => -1.0

Signed-off-by: Uli Schlachter <psychon@znc.in>
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>

src/cairoint.h

@@ -956,7 +956,7 @@ _cairo_restrict_value (double value, double min, double max)
 }
 
 /* C99 round() rounds to the nearest integral value with halfway cases rounded
- * away from 0. _cairo_round rounds halfway cases toward negative infinity.
+ * away from 0. _cairo_round rounds halfway cases toward positive infinity.
  * This matches the rounding behaviour of _cairo_lround. */
 static inline double cairo_const
 _cairo_round (double r)