[PATCH] doc:fix typo in 'mmc write' example

[Shirokov Alexander]

Hello Simon,

Thanks for your answer.Using 0x explicitly shows that we are working with
HEX.
But without the prefix, it looks like a decimal number. And it's more
confusing
when the number of blocks looks like a decimal but is interpreted as HEX.

Here is an example:

    mmc write 0x40000000 0x5000 16
    MMC write: dev # 1, block # 20480, count 22 ... 22 blocks written: OK

This looks better. If we know that all number is HEX by default
    mmc write 40000000 5000 16

Do we have to use something like this?