coccicheck: Add unneeded return variable test

This semantic patch looks for variables that are initialized with a
constant, are never updated, and are only used as parameter of return.
Return the constant instead of using a variable.

Signed-off-by: Peter Senna Tschudin <peter.senna@gmail.com>
Signed-off-by: Michal Marek <mmarek@suse.cz>