There is absolutely no issue here. Although we traditionally use capital letters for only the initial letters of names* and school teachers will tell you it's wrong to do otherwise, the capitalization isn't considered to be part of the spelling. Rather, it's part of the orthography of the langauge, which is the set of conventions we use when writing it down. Thus, "Sabbir Hasan", "SABBIR HASAN" and "SaBbIr HaSaN" are all considered to be the same name. The choice of capitalization is more similar to the choice of a font than a choice of spelling.
* This is a simplification, as Ronald MacDonald, Ludwig van Beethoven and e e cummings will explain.