diag: Use strlcpy/strlcat properly

Currently strlcpy/strlcat are used like strncpy/strncat
in diag driver. The patch corrects the use of strlcpy
and strncpy by passing size as size of destination buffer.

Change-Id: If8f5376413a6f23405e918469c83568c6c73b552
Signed-off-by: Hardik Arya <harya@codeaurora.org>