Revert "ANDROID: mmc: move to a SCHED_FIFO thread"

This reverts commit 52678eee.

This patch instead causes considerable storage performance regressions,
especially as the eMMC goes filled up.

Signed-off-by: Albert I <kras@raphielgang.org>
Signed-off-by: Alexander Winkowski <dereference23@outlook.com>
Change-Id: Ie71cf86738ac609fdb30ab53261519aaa2187ea2