IB/ipath: Future proof eeprom checksum code (contents reading)

In an earlier change, the amount of data read from the flash was
mistakenly limited to the size known to the current driver.  This causes
problems when the length is increased, and written with the new longer
version; the checksum would fail because not enough data was read.
Always read the full 128 byte length to prevent this.

Signed-off-by: Dave Olson <dave.olson@qlogic.com>
Signed-off-by: Roland Dreier <rolandd@cisco.com>