brcm80211: smac: avoid sprom endianess conversions for crc8 check

The data from the sprom consists of u16 values stored in little
endian notation over which a crc8 was determined. To validate this
the buffer needed to be converted for big-endian systems. Reading
the sprom data is now done per byte so conversion is only done
after a successful crc8 check.

Reviewed-by: Alwin Beukers <alwin@broadcom.com>
Reviewed-by: Roland Vossen <rvossen@broadcom.com>
Signed-off-by: Arend van Spriel <arend@broadcom.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>