drm/amd/display: fix memory leaks on error exit return

Currently in the case where some of the allocations fail for dce110_tgv,
dce110_xfmv, dce110_miv or dce110_oppv then the exit return path ends
up leaking allocated objects. Fix this by kfree'ing them before returning.
Also re-work the comparison of the null pointers to use the !ptr idiom.

Detected by CoverityScan, CID#1460246, 1460325, 1460324, 1460392
("Resource Leak")

Fixes: c4562236b3bc ("drm/amd/dc: Add dc display driver (v2)")
Signed-off-by: Colin Ian King <colin.king@canonical.com>
Reviewed-by: Harry Wentland <harry.wentland@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>