sfp: allow cotsworks modules

Cotsworks modules fail the checksums - it appears that Cotsworks
reprograms the EEPROM at the end of production with the final product
information (serial, date code, and exact part number for module
options) and fails to update the checksum.

Work around this by detecting the Cotsworks name in the manufacturer
field, and reducing the checksum failures to warnings rather than a
hard error.

Signed-off-by: Russell King <rmk+kernel@armlinux.org.uk>
Signed-off-by: David S. Miller <davem@davemloft.net>