net: mvpp2: fix possible memory leak

we are allocating memory using kzalloc for struct mvpp2_prs_entry,
but later when we are getting error we were just returning the error
value without releasing the memory.

Signed-off-by: Sudip Mukherjee <sudip@vectorindia.org>
Signed-off-by: David S. Miller <davem@davemloft.net>