octeontx2-af: Fix memory leak of object buf

Currently the error return path when lfs fails to allocate is not free'ing
the memory allocated to buf. Fix this by adding the missing kfree.

Addresses-Coverity: ("Resource leak")
Fixes: f7884097 ("octeontx2-af: Formatting debugfs entry rsrc_alloc.")
Signed-off-by: Colin Ian King <colin.king@canonical.com>
Acked-by: Sunil Goutham <sgoutham@marvell.com>
Signed-off-by: David S. Miller <davem@davemloft.net>