leds: qti-flash: Handle error return path properly

Currently if qti_flash_lmh_mitigation_config() returns an error
in qti_flash_led_strobe(), spin_unlock() is not called in the
error return path. Fix it.

Fixes: 42bdecad ("leds: qti-flash: Fix LMH mitigation configuration")
Change-Id: I1bede93873a151cc9bab7f2000d8f058e1890fda
Signed-off-by: Subbaraman Narayanamurthy <subbaram@codeaurora.org>