mmc: sdhci: fix retuning timer wrongly deleted in sdhci_tasklet_finish

Currently, the retuning timer for retuning mode 1 will be deleted in
function sdhci_tasklet_finish after a mmc request done, which will make
retuning timing never trigger again. This patch fixed this problem.

Signed-off-by: Aaron Lu <Aaron.Lu@amd.com>
Reviewed-by: Philip Rakity <prakity@marvell.com>
Signed-off-by: Chris Ball <cjb@laptop.org>