ssb: Allow reading of 440-byte SPROM that is not rev 4

The current code checks for the special signature that signifies
a revision 4 SPROM. Now that a rev. 8 SPROM with a 440-byte length
has been found that may not have any special code, this check could
be relaxed. With this patch, if the CRC is incorrect for a 256-byte
SPROM, the code will immediately check for a 440-byte SPROM. If there
is still a CRC error, the size is set to 440 bytes, which allows dumping
of most of any 512-byte SPROM if one is encountered.

Signed-off-by: Larry Finger <Larry.Finger@lwfinger.net>
Signed-off-by: Michael Buesch <mb@bu3sch.de>
Signed-off-by: John W. Linville <linville@tuxdriver.com>