[CARBONDATA-3915] Correction in the documentation for spark-shell
[CARBONDATA-3915] Correction in the documentation for spark-shell

Why is this PR needed?
Data load fails because the spark-shell code uses carbonSessions instead of carbonExtensions.

What changes were proposed in this PR?
Have made use of carbonExtensions.

This closes #3866

zzcclp/carbondata,zzcclp/carbondata,zzcclp/carbondata,zzcclp/carbondata,zzcclp/carbondata