rtc: s5m: drop needless struct s5m_rtc_info::i2c member

rtc: s5m: drop needless struct s5m_rtc_info::i2c member

When this driver was converted to using the devres managed i2c device
in commit 7db7ad0817fe ("rtc: s5m: use devm_i2c_new_dummy_device()"),
struct s5m_rtc_info::i2c became essentially unused.

We can drop it from the structure and just use a local temporary
variable, reducing runtime memory consumption by a few bytes.

Reviewed-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Signed-off-by: André Draszik <andre.draszik@linaro.org>
Link: https://lore.kernel.org/r/20250304-rtc-cleanups-v2-2-d4689a71668c@linaro.org
Signed-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>