leds: gpio: Set num_leds after allocation

leds: gpio: Set num_leds after allocation

With the new __counted_by annotation, the "num_leds" variable needs to
valid for accesses to the "leds" array. This requirement is not met in
gpio_leds_create(), since "num_leds" starts at "0", so "leds" index "0"
will not be considered valid (num_leds would need to be "1" to access
index "0").

Fix this by setting the allocation size after allocation, and then update
the final count based on how many were actually added to the array.

Fixes: 52cd75108a42 ("leds: gpio: Annotate struct gpio_leds_priv with __counted_by")
Signed-off-by: Kees Cook <kees@kernel.org>
Reviewed-by: Gustavo A. R. Silva <gustavoars@kernel.org>
Link: https://lore.kernel.org/r/20240716212455.work.809-kees@kernel.org
Signed-off-by: Lee Jones <lee@kernel.org>