mmc: sdhci-of-at91: remove a line of dead code

The goto is correct and the unreachable "return -EINVAL" should be
removed.

Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Acked-by: Ludovic Desroches <ludovic.desroches@atmel.com>
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>