bcma: don't fail for bad SPROM CRC

The brcmsmac driver is now using the bcma SPROM CRC check, which does
not recognize all chipsets that were functional prior to the switch. In
particular, the current code bails out on odd CRC errors in recent
Macbooks. This patch ignores those errors, with the argument that an
unrecognized SPROM should be treated similarly to a non-existing one.

Signed-off-by: Henrik Rydberg <rydberg@euromail.se>
Signed-off-by: John W. Linville <linville@tuxdriver.com>