mmc: android-goldfish: remove logically dead code in goldfish_mmc_irq()

Local variable transfer_error is assigned to a constant value and
it is never updated again.

Remove this variable and the dead code it guards.

Addresses-Coverity-ID: 1222110
Signed-off-by: Gustavo A. R. Silva <garsilva@embeddedor.com>
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>