spi/spi_bfin_sport: drop bits_per_word from client data

Since the member was dropped from the common Blackfin header, we need
to stop using it in the SPORT driver too.

Signed-off-by: Mike Frysinger <vapier@gentoo.org>
Signed-off-by: Scott Jiang <scott.jiang.linux@gmail.com>
Signed-off-by: Grant Likely <grant.likely@secretlab.ca>