drm/gma500: Fix possible out of bounds read

Fix possible out of bounds read, by adding missing comma.
The code may read pass the end of the dsi_errors array
when the most significant bit (bit #31) in the intr_stat register
is set.
This bug has been detected using CppCheck (static analysis tool).

Cc: stable@vger.kernel.org
Signed-off-by: Itai Handler <itai_handler@hotmail.com>
Signed-off-by: Patrik Jakobsson <patrik.r.jakobsson@gmail.com>