igt/gem_lut_handle: Fix errno checking
igt/gem_lut_handle: Fix errno checking

Regression from
commit c1404e05b7477122b9923ba029593c2cb64671a7
Author: Chris Wilson <711c73f64afdce07b7e38039a96d2224209e9a6c@chris-wilson.co.uk>
Date:   Tue Apr 29 07:14:33 2014 +0100

    errno is reset after each syscall

Signed-off-by: Chris Wilson <711c73f64afdce07b7e38039a96d2224209e9a6c@chris-wilson.co.uk>

tiagovignatti/intel-gpu-tools,mv0/intel-gpu-tools,yipdw/intel-gpu-tools,dlespiau/checkmate-test-igt,mv0/intel-gpu-tools,yipdw/intel-gpu-tools,tiagovignatti/intel-gpu-tools,chenxianqin/intel-gpu-tools,erikarn/intel-gpu-tools,dlespiau/checkmate-test-igt,dlespiau/checkmate-test-igt,rib/intel-gpu-tools,rib/intel-gpu-tools,rib/intel-gpu-tools,yipdw/intel-gpu-tools,dlespiau/checkmate-test-igt,erikarn/intel-gpu-tools,rib/intel-gpu-tools,chenxianqin/intel-gpu-tools,erikarn/intel-gpu-tools,tiagovignatti/intel-gpu-tools,tiagovignatti/intel-gpu-tools,erikarn/intel-gpu-tools,mv0/intel-gpu-tools,mv0/intel-gpu-tools,yipdw/intel-gpu-tools,chenxianqin/intel-gpu-tools,chenxianqin/intel-gpu-tools