qbt1000: Terminate fingerprint TA name with null

Terminate the string, coming from userspace and containing the name
of fingerprint trusted app, with null character, to make sure kernel
memory does not leak into logs

Bug: 35644510
Change-Id: I1668a64fcb6747ce3ef3b1ee6321fa5fa4a1798a
CRs-Fixed: 2029409
Signed-off-by: Abir Ghosh <abirg@codeaurora.org>