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 <robert@linux.intel.com>

(cherry picked from commit f40b0d03d796c16c62f4937e99e16de084fc6b9a)

Distrotech/cogl,Distrotech/cogl,Distrotech/cogl,Distrotech/cogl