spi: pl022: Remove set but not used variable 'chip'

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

drivers/spi/spi-pl022.c: In function 'do_polling_transfer':
drivers/spi/spi-pl022.c:1493:20: warning:
 variable 'chip' set but not used [-Wunused-but-set-variable]

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