drivers/rtc/rtc-tps65910.c: use platform_get_irq() to get RTC irq details

As RTC driver needs only irq number from platform data, using
platform_get_irq(), instead of generic dev_get_platdata().

Signed-off-by: Venu Byravarasu <vbyravarasu@nvidia.com>
Acked-by: Stephen Warren <swarren@wwwdotorg.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>