spi/spi-fsl-spi: reference correct pdata in fsl_spi_cs_control

spi/spi-fsl-spi: reference correct pdata in fsl_spi_cs_control

Commit 178db7d3, "spi: Fix device unregistration when unregistering
the bus master", changed spi device initialization of dev.parent pointer
to be the master's device pointer instead of his parent.

This introduced a bug in spi-fsl-spi, since its usage of spi device
pointer was not updated accordingly. This was later fixed by commit
5039a86, "spi/mpc83xx: fix NULL pdata dereference bug", but it missed
another spot on fsl_spi_cs_control function where we also need to update
usage of spi device pointer. This change address that.

Cc: stable@vger.kernel.org
Signed-off-by: Herton Ronaldo Krzesinski <herton.krzesinski@canonical.com>
Acked-by: Joakim Tjernlund <Joakim.Tjernlund@transmode.se>
Signed-off-by: Grant Likely <grant.likely@secretlab.ca>