spi: omap-100k: Remove set but not used variable 'dataH'

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

drivers/spi/spi-omap-100k.c: In function spi100k_read_data:
drivers/spi/spi-omap-100k.c:140:6: warning: variable dataH set but not used [-Wunused-but-set-variable]

It is not used since commit 35c9049b

 ("Add OMAP spi100k driver")

Reported-by: Hulk Robot <hulkci@huawei.com>
Signed-off-by: zhengbin <zhengbin13@huawei.com>
Link: https://lore.kernel.org/r/1570581437-104549-2-git-send-email-zhengbin13@huawei.com
Signed-off-by: Mark Brown <broonie@kernel.org>