framebuffer: Annotate the output parameter of get_viewport4fv()
framebuffer: Annotate the output parameter of get_viewport4fv()

Annotate that the float* is an out parameter that points to a caller
allocated array of 4 floats.

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

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