mmc: atmel: don't test host->data

Found using smatch:
drivers/mmc/host/atmel-mci.c:827 atmci_pdc_complete() warn: variable
dereferenced before check 'host->data' (see line 807)

Stop testing host->data as it is not NULL at that point.

Signed-off-by: Alexandre Belloni <alexandre.belloni@free-electrons.com>
Acked-by: Ludovic Desroches <ludovic.desroches@atmel.com>
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>
Signed-off-by: Chris Ball <chris@printf.net>