mmc: pwrseq: Fix error code propagation in mmc_pwrseq_simple_alloc()

If the struct mmc_pwrseq_match .alloc function used to allocate a
struct mmc_pwrseq fails, the error is propagated to mmc_of_parse().

But instead of returning the error code in pwrseq, host->pwrseq is
returned which will always be 0. So mmc_of_parse() succeeds even if
the pwrseq .alloc function failed and host->pwrseq is NULL.

This makes the SDIO device to not be powered if the power sequencing
.alloc functions wants to be deferred due a missing resource because
the mmc controller driver probe did wrongly succeed.

Fixes: 0f12a0ce ("mmc: pwrseq: simplify alloc/free hooks")
Signed-off-by: Javier Martinez Canillas <javier.martinez@collabora.co.uk>
Reviewed-by: Alexandre Courbot <acourbot@nvidia.com>
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>