mmc: sdhci-of-dwcmshc: th1520: Increase tuning loop count to 128

Fix SD card tuning error by increasing tuning loop count
from 40(MAX_TUNING_LOOP) to 128.

For some reason the tuning algorithm requires to move through all the taps
of delay line even if the THRESHOLD_MODE (bit 2 in AT_CTRL_R) is used
instead of the LARGEST_WIN_MODE.

Tested-by: Drew Fustini <drew@pdp7.com>
Tested-by: Xi Ruoyao <xry111@xry111.site>
Signed-off-by: Maksim Kiselev <bigunclemax@gmail.com>
Acked-by: Adrian Hunter <adrian.hunter@intel.com>
Fixes: 43658a54

 ("mmc: sdhci-of-dwcmshc: Add support for T-Head TH1520")
Cc: stable@vger.kernel.org
Link: https://lore.kernel.org/r/20240402093539.184287-1-bigunclemax@gmail.com
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>