spi: ti-qspi: Fix getting correct address for qspi

Now platform_get_drvdata() returns the address of qspi rather than master.
Also drop unneeded spi_unregister_master() call in ti_qspi_remove() because
we use devm_spi_register_master() in probe.

commit cbcabb7a "spi/qspi: Fix qspi remove path" assumes
platform_get_drvdata() returns address of master. However,
commit 160a0613 "spi/qspi: set correct platform drvdata in ti_qspi_probe()"
pass qspi to platform_set_drvdata().

Signed-off-by: Axel Lin <axel.lin@ingics.com>
Reviewed-by: Sourav Poddar <sourav.poddar@ti.com>
Signed-off-by: Mark Brown <broonie@linaro.org>