Input: joystick - use sizeof(*pointer) instead of sizeof(type)

Input: joystick - use sizeof(*pointer) instead of sizeof(type)

It is preferred to use sizeof(*pointer) instead of sizeof(type)
due to the type of the variable can change and one needs not
change the former (unlike the latter).

At the same time refactor the code to not use assignment in "if"
conditions.

This patch has no effect on runtime behavior.

Signed-off-by: Erick Archer <erick.archer@outlook.com>
Link: https://lore.kernel.org/r/AS8PR02MB7237FEA55FAC8A9453F2DA6F8BC42@AS8PR02MB7237.eurprd02.prod.outlook.com
Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>