i2c: slave eeprom: clean up sysfs bin attribute read()/write()

The change removes redundant sysfs binary file boundary checks,
since this task is already done on caller side in fs/sysfs/file.c

Note, on file size overflow read() now returns 0, and this is a
correct and expected EOF notification according to POSIX.

Signed-off-by: Vladimir Zapolskiy <vz@mleia.com>
Signed-off-by: Wolfram Sang <wsa@the-dreams.de>