Modify Used Capacity Unit Conversion Error

[luojiagen]

What this PR does / why we need it:

Which issue this PR fixes (optional, in fixes #<issue number>(, fixes #<issue_number>, ...) format, will close that issue when PR gets merged): fixes #

Special notes for your reviewer:

Release note:

[codecov]

Codecov Report

Merging #632 (c3f0756) into vplex_20230329 (f2765e1) will decrease coverage by 0.01%.
The diff coverage is 35.29%.

@@                Coverage Diff                 @@
##           vplex_20230329     #632      +/-   ##
==================================================
- Coverage           70.85%   70.85%   -0.01%     
==================================================
  Files                 195      195              
  Lines               23987    24001      +14     
  Branches             3674     3678       +4     
==================================================
+ Hits                16997    17006       +9     
- Misses               5826     5833       +7     
+ Partials             1164     1162       -2     

Impacted Files	Coverage Δ
delfin/drivers/dell_emc/vplex/vplex_stor.py	77.68% <35.29%> (-1.68%)	⬇️

... and 1 file with indirect coverage changes