docs: fix javadoc for deferred uni creation

[manofthepeace]

from().value() does not exist.

[codecov]

Codecov Report

Merging #1440 (f287ac7) into main (fb2f908) will decrease coverage by 0.12%.
Report is 1 commits behind head on main.
The diff coverage is n/a.

Additional details and impacted files

@@             Coverage Diff              @@
##               main    #1440      +/-   ##
============================================
- Coverage     89.40%   89.28%   -0.12%     
  Complexity     3367     3367              
============================================
  Files           459      459              
  Lines         13454    13454              
  Branches       1655     1655              
============================================
- Hits          12029    12013      -16     
- Misses          792      803      +11     
- Partials        633      638       +5     

Files	Coverage Δ
...entation/src/main/java/io/smallrye/mutiny/Uni.java	90.90% <ø> (ø)

... and 11 files with indirect coverage changes

[jponge]

Good catch 😄