Let's change the function signature to return the pointer to memory or
an error pointer on failure, and take an argument that lets us return
the size of the aux data read. This way we can remove the
cmd_db_read_aux_data_len() API entirely and also get rid of the memcpy
operation from cmd_db to the caller. Updating the only user of this code
shows that making this change allows us to remove a function and put the
lookup where the user is.

Cc: Mahesh Sivasubramanian <msivasub@codeaurora.org>
Cc: Lina Iyer <ilina@codeaurora.org>
Cc: Bjorn Andersson <bjorn.andersson@linaro.org>
Cc: Evan Green <evgreen@chromium.org>
Cc: Jordan Crouse <jcrouse@codeaurora.org>
Cc: Rob Clark <robdclark@gmail.com>
Signed-off-by: Stephen Boyd <swboyd@chromium.org>
Signed-off-by: Andy Gross <andy.gross@linaro.org>