leds: qpnp-flash-v2: Fix safety timer configuration

The mask and enable values being used are incorrect for the
safety timer. Fix it. Also take this opportunity to update
all relevant macros to use the GENMASK(h,l)/BIT(x) macros.

CRs-Fixed: 1024187
Change-Id: Ibdd139c98aa289f1d6b8545b953e79a1187284e9
Signed-off-by: Devesh Jhunjhunwala <deveshj@codeaurora.org>