diag: Fix writing of error message for mode command

Currently, when a mode command that is not the mode reset command
is sent, a kernel error message is written. This is wrongfully written.
Make changes so that when a mode command is sent that is not the
mode reset command, an error message is not wrongfully written.

Change-Id: I07666d5cda3c63804cc1dffc7cf1672915c02c1f
Signed-off-by: Dixon Peterson <dixonp@codeaurora.org>