modesetting: Don't free(dst) in drmmode_prop_info_copy

The destination is always either on the stack or in the middle of some
struct.

Signed-off-by: Adam Jackson <ajax@redhat.com>
1 job for ms-bad-free in 2 minutes and 41 seconds (queued for 1 second)
Status Job ID Name Coverage
  Test
passed #26236
job

00:02:41