[U-Boot] [RFC] mmc:fix: Increase the timeout value for SDHCI_send_command()

[Lukasz Majewski]

I'd like to ask for your opinion about the following problem:

TRATS # saveenv
Saving Environment to MMC...
Writing to MMC(0)... Controller never released inhibit bit(s).
Controller never released inhibit bit(s).
Controller never released inhibit bit(s).
...
failed

The same is for e.g. ext4.

The provided patch seems to solve the problem, but I DO NOT think that
increasing delay is an acceptable solution to any problem.