clocksource/drivers/sun5i: Handle error returns from devm_reset_control_get_optional_...

clocksource/drivers/sun5i: Handle error returns from devm_reset_control_get_optional_exclusive()

The devm_reset_control_get_optional_exclusive() function may return an
ERR_PTR in case of genuine reset control acquisition errors, not just
NULL which indicates the legitimate absence of an optional reset.

Add an IS_ERR() check after the call in sun5i_timer_probe(). On error,
return the error code to ensure proper failure handling rather than
proceeding with invalid pointers.

Fixes: 7e5bac610d2f ("clocksource/drivers/sun5i: Convert to platform device driver")
Signed-off-by: Chen Ni <nichen@iscas.ac.cn>
Signed-off-by: Daniel Lezcano <daniel.lezcano@kernel.org>
Acked-by: Chen-Yu Tsai <wens@kernel.org>
Link: https://patch.msgid.link/20260205084037.3661261-1-nichen@iscas.ac.cn