diag: Fix incorrect checks in diag driver

Diag driver checks for a particular error value when it tries
to read from the HSIC channel. However, there is a possibility
for HSIC driver to return any error code.

Change-Id: I9f9f2680fbb86cb7ea1eb58b472f2a9bfb150226
Signed-off-by: Ravi Aravamudhan <aravamud@codeaurora.org>