diag: Do not clear masks during logging mode switch

Currently, masks will be cleared during logging mode
switch if physical USB disconnection will happen in
concurrency. There is no need to clear the masks in
logging switch case. The patch ensures that masks
will be cleared only in valid cases.

Change-Id: I68f5335c4fa8fe06ba1f686f29336a8150991368
Signed-off-by: Mohit Aggarwal <maggarwa@codeaurora.org>