msm: vidc: Fix crash issue on SYS_ERROR response from FW.

FW writes debug info into SFR register when it crashes.
Target crashes when driver dumps SFR register on SYS_ERROR,
since FW writes string with debug info into the SFR register
without null terminator.
Fix the issue by adding null terminator to the sfr buffer string
if its not present.

Change-Id: I13767b9826b6d1d915a52b897a627d5082fba9c4
CRs-fixed: 589482
Signed-off-by: Jayasena Sangaraboina <jsanga@codeaurora.org>