diag: Rectify wait condition while reading over peripherals

While reading data over smd leads to infinite looping due to
incorrect wait condition. Also, there is no need to queue a
read until DATA event notification is received from smd.

Change-Id: Ibbd4d44f32adce362e9d44fc392c40543965403b
Signed-off-by: Katish Paran <kparan@codeaurora.org>