Matrix elements cannot be accessed with dot notation.

Change-Id: I48258428e3fa5ffe9c95a8983516433b98ce233a
Reviewed-on: https://swiftshader-review.googlesource.com/13629Tested-by: Nicolas Capens <nicolascapens@google.com>
Reviewed-by: Alexis Hétu <sugoi@google.com>
Reviewed-by: Nicolas Capens <nicolascapens@google.com>