tools/cgget: fix a resource leak get_cv_value()

tools/cgget: fix a resource leak get_cv_value()

Fix a resource leak in get_cv_value(), reported by Coverity tool:

CID 258291 (#1 of 1): Resource leak (RESOURCE_LEAK). leaked_storage:
Variable handle going out of scope leaks the storage it points to.

failure on the realloc(), doesn't free the *handle. Fix it by using
the goto read_end(), that does the job of freeing the handle.

Suggested-by: Tom Hromatka <tom.hromatka@oracle.com>
Signed-off-by: Kamalesh Babulal <kamalesh.babulal@oracle.com>
Signed-off-by: Tom Hromatka <tom.hromatka@oracle.com>