drm/i915/gem: remove redundant assignments to variable ret

The variable ret is being assigned with a value that is never read
both before and after a while-loop. The variable is being re-assigned
inside the while-loop and afterwards on the call to the function
i915_gem_object_lock_interruptible. Remove the redundants assignments.

Cleans up clang scan-build warnings:

warning: Although the value stored to 'ret' is used in the
enclosing expression, the value is never actually read
from 'ret' [deadcode.DeadStores]

warning: Value stored to 'ret' is never read [deadcode.DeadStores]

Signed-off-by: Colin Ian King <colin.i.king@gmail.com>
Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Signed-off-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20221007194745.2749277-1-colin.i.king@gmail.com