Fix a warning when building the SDL2 winsys
Fix a warning when building the SDL2 winsys

The SDL2 winsys was using _cogl_set_error without including its header
so it was giving an annoying warning. This patch also fixes some
indentation issues.

Reviewed-by: Robert Bragg <12e9293ec6b30c7fa8a0926af42807e929c1684f@linux.intel.com>

gcampax/cogl,gcampax/cogl,gcampax/cogl,djdeath/cogl-android,djdeath/cogl,djdeath/cogl,djdeath/cogl-android,gcampax/cogl,djdeath/cogl,djdeath/cogl-android