linux: do not autoload sdhci.ko as sdhci-pltfm.ko already depends on it

Currently, installing kmod-sdhci fails with "sdhci is already loaded" since
"sdhci.ko" is inserted explicitely first, the implicitely loaded again when
"sdhci-pltfm.ko" is inserted as the latter depends on the former.

Remove the explicit autoprobe of "sdhci.ko" to fix the postinstall script.

Acked-by: John Crispin <john@phrozen.org>
Signed-off-by: Jo-Philipp Wich <jo@mein.io>