spi: spi-gpio: Remove set but not used variable 'pdata'

Fixes gcc '-Wunused-but-set-variable' warning:

drivers/spi/spi-gpio.c: In function 'spi_gpio_remove':
drivers/spi/spi-gpio.c:450:33: warning:
 variable 'pdata' set but not used [-Wunused-but-set-variable]

Signed-off-by: YueHaibing <yuehaibing@huawei.com>
Signed-off-by: Mark Brown <broonie@kernel.org>