misc/93xx46: avoid infinite loop on write()

This change fixes a problem of infinite zero byte write() without
an error status, if there is an attempt to write a file bigger than
EEPROM size over sysfs interface.

Signed-off-by: Vladimir Zapolskiy <vladimir_zapolskiy@mentor.com>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>