i2c-designware: i2c_dw_read: Use "struct dw_i2c_dev" pointer

We don't have to use "struct i2c_adapter" pointer here.
Let's use a local "struct dw_i2c_dev" pointer, instead.

Signed-off-by: Shinya Kuribayashi <shinya.kuribayashi@necel.com>
Acked-by: Baruch Siach <baruch@tkos.co.il>
Signed-off-by: Ben Dooks <ben-linux@fluff.org>