Input: iqs5xx - use local input_dev pointer

Both iqs5xx_axis_init() and iqs5xx_irq() already define a local
input_dev pointer 'input'. Use this instead of iqs5xx->input so
as to make the code a bit smaller.

Signed-off-by: Jeff LaBundy <jeff@labundy.com>
Link: https://lore.kernel.org/r/20220320025707.404544-1-jeff@labundy.com
Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>