octeontx2-vf: fix bitmap leak

The bitmap allocated with bitmap_zalloc() in otx2vf_probe() was not
released in otx2vf_remove(). Unbinding and rebinding the driver therefore
triggers a kmemleak warning:

    unreferenced object (size 8):
      backtrace:
        bitmap_zalloc
        otx2vf_probe

Call bitmap_free() in the remove path to fix the leak.

Fixes: efabce29 ("octeontx2-pf: AF_XDP zero copy receive support")
Signed-off-by: Bo Sun <bo@mboxify.com>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>