soc: qcom: pil: NULL check before pil_memset_io

In existing implementation if vmap fails device panics for
NULL pointer access while doing pil_memset_io.
Instead check for the NULL pointer.

Change-Id: I1b9fd084a8c168b70f6e01134e4122445e4873b4
Signed-off-by: Swetha Chikkaboraiah <schikk@codeaurora.org>