staging: unisys: visorchannel: Improved cleanup code

kfree on NULL pointer is a no-op.

This patch used the following semantic patch to find an instance where NULL
check is present before kfree

// <smpl>
@@ expression E; @@
- if (E != NULL) { kfree(E); }
+ kfree(E);
@@ expression E; @@
- if (E != NULL) { kfree(E); E = NULL; }
+ kfree(E);
+ E = NULL;
// </smpl>

Code is made more simpler by breaking up of sequence of kmallocs and adding
some more exit labels.
Removed unnecessary initialization of buf and fmtbuf to NULL as they are local
variables.

Suggested-by: Arnd Bergmann <arnd@arndb.de>
Suggested-by: Julia Lawall <julia.lawall@lip6.fr>
Signed-off-by: Tapasweni Pathak <tapaswenipathak@gmail.com>
Acked-by: Julia Lawall <julia.lawall@lip6.fr>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>