icnss: NULL terminate the fw build timestamp string

If fw build timestamp passed by QMI is a non-NULL terminated string,
it might result in a out-of-bounds read in icnss_get_soc_info. Hence,
manually NULL terminate the string.

Change-Id: I252196cd12784d841b29303c42591efc59da64f1
CRs-Fixed: 2322317
Signed-off-by: Yuanyuan Liu <yuanliu@codeaurora.org>