[SCSI] lib: string_get_size(): don't hang on zero; no decimals on exact

We would hang forever when passing a zero to string_get_size().
Furthermore, string_get_size() would produce decimals on a value small
enough to be exact.  Finally, a few formatting issues are inconsistent
with standard SI style guidelines.

- If the value is less than the divisor, skip the entire rounding
  step.  This prints out all small values including zero as integers,
  without decimals.
- Add a space between the value and the symbol for the unit,
  consistent with standard SI practice.
- Lower case k in kB since we are talking about powers of 10.
- Finally, change "int" to "unsigned int" in one place to shut up a
  gcc warning when compiling the code out-of-kernel for testing.

Signed-off-by: H. Peter Anvin <hpa@zytor.com>
Signed-off-by: James Bottomley <James.Bottomley@HansenPartnership.com>