leds: leds-qpnp-flash: amend strobe bit for hardware strobe

Hardware strobe bit is bit[2] per PMIC hardware specification. This
bit should be set when user writes to existing sysfs entry to enable
hardware strobe.

Change-Id: I3d7bda808997025c1716f459807011da83ee1eb7
Signed-off-by: Jigarkumar Kishorkumar Zala <j_zala@codeaurora.org>
Signed-off-by: Chun Zhang <chunz@codeaurora.org>