mmc: meson-mx-sdio: check devm_kasprintf for failure

devm_kasprintf() may return NULL on failure of internal allocation thus
the assignments to  init.name  are not safe if not checked. On error
meson_mx_mmc_register_clks() returns negative values so -ENOMEM in the
(unlikely) failure case of devm_kasprintf() should be fine here.

Signed-off-by: Nicholas Mc Guire <hofrat@osadl.org>
Fixes: ed80a13b ("mmc: meson-mx-sdio: Add a driver for the Amlogic Meson8 and Meson8b SoCs")
Acked-by: Martin Blumenstingl <martin.blumenstingl@googlemail.com>
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>