qcom: subsys-pil-tz: Modify arguments to a min() macro check

sizeof() may not return the same type on all architectures.
Use the fixed buffer length of the failure reason buffer
as the argument to the min macro instead of using sizeof.

Change-Id: I1700f3ec49e6c3cc595ef91b74a75fb8590d7a2c
Signed-off-by: Vikram Mulukutla <markivx@codeaurora.org>