msm: mdss: dsi: ignore error interrupt when mask not set

Ignore handling error interrupt when error intr mask is not set,
as we do not expect it to be generated.

Change-Id: Iabe58f2a67ddbd0c7628fdf2d830568ff0e3b013
Signed-off-by: Veera Sundaram Sankaran <veeras@codeaurora.org>