rtc-twl4030: Fix periodic interrupt

rtc-twl4030: Fix periodic interrupt

RTC generates an extra spurious interrupt for every actual periodic
interrupt. This is due to a problem with the RTC_IT bit of
REG_PWR_ISR1. It requires two writes or two reads (when COR is
enabled) to clear it. Since COR is enabled and one read of the same
register is done already (inside twl4030-pwrirq.c do_twl4030_pwrirq()
function), we can do away with a need to add one more write into the
same register inside the interrupt handler, by replacing the write
currently present with just one extra read.

Signed-off-by: Jagadeesh Bhaskar Pakaravoor <j-pakaravoor@ti.com>
Signed-off-by: Tony Lindgren <tony@atomide.com>