[U-Boot] [PATCH] cmd_mmc: fix bootpart-resize maxarg to 4

[DEATHX]

sorry for send this patch two times, It shows being held until the list
moderator can review it for approval.

I think maybe I didn't register the correct mail address and sent it
again. but it still show wait for moderator review.

At last I register my private mail address to this list and found I have
post the same post two time. 

I'm so sorry for this mistake.

Wally