[PATCH] I2C: ds1337: i2c_transfer() checking

i2c_transfer returns number of sucessfully transfered messages. Change
error checking to accordingly. (ds1337_set_datetime never returned
sucess)

Signed-off-by: Ladislav Michl <ladis@linux-mips.org>
Signed-off-by: James Chapman <jchapman@katalix.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>