drivers: gpu: Remove unused function in ttm_lock.c
drivers: gpu: Remove unused function in ttm_lock.c

Remove unused function ttm_write_lock_downgrade() from
drm/ttm/ttm_lock.c.

This eliminates the following warning in drm/ttm/ttm_lock.c:
drivers/gpu/drm/ttm/ttm_lock.c:189:6: warning: no previous prototype for ‘ttm_write_lock_downgrade’ [-Wmissing-prototypes]

Signed-off-by: Rashika Kheria <62a2cbd3422b0d621dafb7ceeff40187aeaed4ed@gmail.com>
Reviewed-by: Josh Triplett <c028c213ed5efcf30c3f4fc7361dbde0c893c5b7@joshtriplett.org>
Reviewed-by: Thomas Hellstrom <a26490dfbee4be3d38287ad6448444504f58193c@vmware.com>

KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs