Refs #492. Fixed c/zsyr bug with negative incx.

Author: xianyi

interface/zsyr.c

@@ -173,7 +173,7 @@ void CNAME(enum CBLAS_ORDER order, enum CBLAS_UPLO Uplo, int n, FLOAT alpha, FLO
 
   FUNCTION_PROFILE_START();
 
-  if (incx < 0 ) x -= (n - 1) * incx;
+  if (incx < 0 ) x -= (n - 1) * incx * 2;
 
   buffer = (FLOAT *)blas_memory_alloc(1);