Input: adi - remove redundant variable z

Input: adi - remove redundant variable z

Variable z is being assigned a value that is never read, the
variable is redundant and can be removed.

Cleans up clang scan build warning:
drivers/input/joystick/adi.c:139:6: warning: Although the
value stored to 'z' is used in the enclosing expression,
the value is never actually read from 'z' [deadcode.DeadStores]

Signed-off-by: Colin Ian King <colin.i.king@gmail.com>
Link: https://lore.kernel.org/r/20220318002318.80519-1-colin.i.king@gmail.com
Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>