drivers: qcom: Add declaration of msm_timer_get_sclk_ticks

Add declaration of msm_timer_get_sclk_ticks to boot_stats.h
to allow reference from other files.

Change-Id: I4f1980cf03c362474babde270d4656eeb1593993
Signed-off-by: Shreyas K K <shrekk@codeaurora.org>