i2c: fsl_i2c: i2c_read(): dont try to write address w/ alen=0

if alen is 0: no longer start a write cycle before reading data.

Signed-off-by: Dirk Eibach <dirk.eibach@gdsys.cc>
Signed-off-by: Reinhard Pfau <reinhard.pfau@gdsys.cc>
Acked-by: Heiko Schocher <hs@denx.de>
Signed-off-by: Andy Fleming <afleming@freescale.com>