mmc: host: tmio: drop superfluous exit path

The probe exit path on error does nothing since commit 94b110af
("mmc: tmio: add tmio_mmc_host_alloc/free()"), so we can bail out
immediately.

Signed-off-by: Wolfram Sang <wsa+renesas@sang-engineering.com>
Reviewed-by: Simon Horman <horms+renesas@verge.net.au>
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>