[DRIVER] dw-mmc: spl: modify the timeout for reading data to 50ms

Based on a patch suggested by rockchip after having issues testing E09 at -37°C: boot failed with the following error:

MMC error: The cmd index is 16, ret is -110.....
*** ERROR: Can't read MBR header ***
part_get_info_efi: *** ERROR: Invalid GPT ***
MMC error: The cmd index is 16, ret is -110.....
*** ERROR: Can't read MBR header ***
part_get_info_efi: *** ERROR: Invalid Backup GPT ***
MMC error: The cmd index is 16, ret is -110.....
*** ERROR: Can't read MBR header ***
part_get_info_efi: *** ERROR: Invalid GPT ***
MMC error: The cmd index is 16, ret is -110.....
*** ERROR: Can't read MBR header ***
part_get_info_efi: *** ERROR: Invalid Backup GPT ***

Original commit message:

KOWIN's EMMC has a timeout issue and needs to be increased. bug:

[2024-05-07_16:55:54:251]MMC error: The cmd index is 18, ret is -110
[2024-05-07_16:55:54:282]MMC error: The cmd index is 7, ret is -110
[2024-05-07_16:55:54:297]MMC error: The cmd index is 7, ret is -110

This patch depends on upstream commit https://github.com/rockchip-linux/u-boot/commit/bbd0d60085f5ef194a4eceb07f525c3b97ccff1b which is included in this MR