common-utils: make vector a const parameter

To avoid the warning and preparing for adding writesame support.

Updates: #617
Change-Id: I0710b1e4c240368a9bf52968bddc6e250ae2028d
Signed-off-by: Xiubo Li <xiubli@redhat.com>

libglusterfs/src/glusterfs/common-utils.h

@@ -669,7 +669,7 @@ mem_0filled(const char *buf, size_t size)
 }
 
 static inline int
-iov_0filled(struct iovec *vector, int count)
+iov_0filled(const struct iovec *vector, int count)
 {
     int i = 0;
     int ret = 0;