Input: rearrange input_alloc_device() to prepare for preallocating of vals

In preparation to have dev->vals memory pre-allocated rearrange
code in input_alloc_device() so that it allows handling multiple
points of failure.

Reviewed-by: Jeff LaBundy <jeff@labundy.com>
Reviewed-by: Benjamin Tissoires <bentiss@kernel.org>
Link: https://lore.kernel.org/r/20240703213756.3375978-6-dmitry.torokhov@gmail.com


Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>