adreno_tz: Remove unnecessary devfreq NULL check in tz_handler()

Caller of tz_handler() is having the NULL check for devfreq,So
we don’t need unnecessary NULL pointer check.

CRs-Fixed: 2046922
Change-Id: I42eb70ab19b4a5af193521d77bca86447a1ecdb8
Signed-off-by: Hareesh Gundu <hareeshg@codeaurora.org>
Signed-off-by: Abhilash Kumar <krabhi@codeaurora.org>