drm/i915/gem: Remove some unnecessary code

The test for vma should always return true, and when assigning -EBUSY
to ret, the variable should already have that value.

Signed-off-by: Thomas Hellström <thomas.hellstrom@linux.intel.com>
Reviewed-by: Niranjana Vishwanathapura <niranjana.vishwanathapura@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20220304082641.308069-4-thomas.hellstrom@linux.intel.com