diag: Donot queue read in error case during mhi diag open

Donot queue any mhi diag read work when there is an error while
opening mhi diag channels.

Change-Id: Ie4a058b755dbdba7a3d12a19aebdc8f2e059e8ae
Signed-off-by: Sreelakshmi Gownipalli <sgownipa@codeaurora.org>