drm/radeon/r600_cs: Few typo fixes

s/miror/mirror/
s/needind/needing/
s/informations/information/

Acked-by: Randy Dunlap <rdunlap@infradead.org>
Signed-off-by: Bhaskar Chowdhury <unixbhaskar@gmail.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>