drivers/rtc/rtc-ds2404.c: use module_platform_driver macro

Remove removes some code duplication by using module_platform_driver().

Signed-off-by: Srinivas Kandagatla <srinivas.kandagatla@st.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>