diag: Prevent using uninitialized mdlog session mask

Add check to prevent using uninitialized session mask to translate
kernel to user mask. Also remove unused macro definition for SMUX.

Change-Id: I341f0308775a2c5a00856fe6ec8acf9b63e207d9
Signed-off-by: Manoj Prabhu B <bmanoj@codeaurora.org>