media: ov5640: add error trace in case of i2c read failure

Add an error trace in ov5640_read_reg() in case of i2c_transfer()
failure.
Uniformize error traces using dev_err instead v4l2_err.

Signed-off-by: Hugues Fruchet <hugues.fruchet@st.com>
Signed-off-by: Sakari Ailus <sakari.ailus@linux.intel.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>