Annotate int2float() as being a pure function.

This allows gcc to fold duplicate calls into a single call.  Since
the current users do actually call it multiple times with the
same arguments, this is an obvious win.

Signed-off-by: Steven Fuerst <svfuerst@gmail.com>

diff --cc drivers/gpu/drm/radeon/r600_blit.c
Simple merge

diff --cc drivers/gpu/drm/radeon/r600_blit_shaders.h
Simple merge