net: stmmac: fix memory leak during driver probe

On driver probe, kmemleak reported the following memory leak which was
due to allocated bitmap that was not being freed in stmmac_dvr_probe().

unreferenced object 0xffff9276014b13c0 (size 8):
  comm "systemd-udevd", pid 2143, jiffies 4294681112 (age 116.720s)
  hex dump (first 8 bytes):
    00 00 00 00 00 00 00 00                          ........
  backtrace:
    [<00000000c51e34b2>] stmmac_dvr_probe+0x1c0/0x440 [stmmac]
    [<00000000b530eb41>] intel_eth_pci_probe.cold+0x2b/0x14e [dwmac_intel]
    [<00000000b10f8929>] pci_device_probe+0xd2/0x150
    [<00000000fb254c74>] really_probe+0xf8/0x410
    [<0000000034128a59>] driver_probe_device+0x5d/0x150
    [<00000000016104d5>] device_driver_attach+0x53/0x60
    [<00000000cb18cd07>] __driver_attach+0x96/0x140
    [<00000000da9ffd5c>] bus_for_each_dev+0x7a/0xc0
    [<00000000af061a88>] bus_add_driver+0x184/0x1f0
    [<000000008be5c1c5>] driver_register+0x6c/0xc0
    [<0000000052b18a9e>] do_one_initcall+0x4d/0x210
    [<00000000154d4f07>] do_init_module+0x5c/0x230
    [<000000009b648d09>] load_module+0x2a5a/0x2d40
    [<000000000d86b76d>] __do_sys_finit_module+0xb5/0x120
    [<000000002b0cef95>] do_syscall_64+0x33/0x40
    [<0000000067b45bbb>] entry_SYSCALL_64_after_hwframe+0x44/0xa9

Fixes: bba2556e ("net: stmmac: Enable RX via AF_XDP zero-copy")
Cc: Ong Boon Leong <boon.leong.ong@intel.com>
Signed-off-by: Wong Vee Khee <vee.khee.wong@linux.intel.com>
Signed-off-by: David S. Miller <davem@davemloft.net>