mmc: host: omap_hsmmc: return on fatal errors from omap_hsmmc_reg_get

Now return error only if the return value of
devm_regulator_get_optional() is not the same as -ENODEV, since with
-EPROBE_DEFER, the regulator can be obtained later and all other
errors are fatal.

Signed-off-by: Kishon Vijay Abraham I <kishon@ti.com>
Tested-by: Tony Lindgren <tony@atomide.com>
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>