asoc: codecs: Fix out of bounds access in register show function

In register show function, when snprintf returns a negative value
out of bounds access occurs while copying the data to user.
Add return value check on snprintf before copy_to_user
to fix this and add sizeof() for tmp_buff to avoid buffer
overflow.

Change-Id: I15f1add37987d2176a165669d7a5b40bd576004c
Signed-off-by: Prasad Kumpatla <nkumpat@codeaurora.org>