docs: Fix column name in gpload example

Discussion: https://github.com/greenplum-db/gpdb/pull/5155Co-authored-by: NDaniel Gustafsson <dgustafsson@pivotal.io>

gpMgmt/doc/gpload_help

@@ -608,7 +608,7 @@ GPLOAD:
            - name: text
            - amount: float4
            - category: text
-           - desc: text
+           - descr: text
            - date: date
     - FORMAT: text
     - DELIMITER: '|'

gpdb-doc/dita/admin_guide/load/topics/g-loading-data-with-gpload.xml

@@ -46,7 +46,7 @@ GPLOAD:
            - name: text
            - amount: float4
            - category: text
-           - desc: text
+           - descr: text
            - date: date
     - FORMAT: text
     - DELIMITER: '|'