Fix integer truncation warnings from Clang

ssize_t assignment to couchstore_error_t requires explicit cast
since it's throwing away the upper half of a 64-bit value.

Change-Id: If4456dcb1a8fd34234bde433d30d2441c6dcb90d
Reviewed-on: http://review.couchbase.org/19179
Tested-by: Aaron Miller <apage43@ninjawhale.com>
Reviewed-by: Aaron Miller <apage43@ninjawhale.com>

src/couch_file_write.c

@@ -66,14 +66,14 @@ couchstore_error_t db_write_header(Db *db, sized_buf *buf, off_t *pos)
 
     written = db->file_ops->pwrite(db->file_handle, &headerbuf, sizeof(headerbuf), write_pos);
     if (written < 0) {
-        return written;
+        return (couchstore_error_t)written;
     }
     write_pos += written;
 
     //Write actual header
     written = raw_write(db, buf, write_pos);
     if (written < 0) {
-        return written;
+        return (couchstore_error_t)written;
     }
     write_pos += written;
     db->file_pos = write_pos;
@@ -97,14 +97,14 @@ int db_write_buf(Db *db, const sized_buf *buf, off_t *pos, size_t *disk_size)
     sized_buf sized_headerbuf = { headerbuf, 8 };
     written = raw_write(db, &sized_headerbuf, end_pos);
     if (written < 0) {
-        return written;
+        return (int)written;
     }
     end_pos += written;
 
     // Write actual buffer:
     written = raw_write(db, buf, end_pos);
     if (written < 0) {
-        return written;
+        return (int)written;
     }
     end_pos += written;