NFSv4: Add an fattr allocation to _nfs4_discover_trunking()

NFSv4: Add an fattr allocation to _nfs4_discover_trunking()

This was missed in 254a37718b3f ("NFSv4: Fix free of uninitialized
nfs4_label on referral lookup.") and causes a panic when mounting
with '-o trunkdiscovery':

PID: 1604   TASK: ffff93dac3520000  CPU: 3   COMMAND: "mount.nfs"
 #0 [ffffb79140f738f8] machine_kexec at ffffffffaec64bee
 #1 [ffffb79140f73950] __crash_kexec at ffffffffaeda67fd
 #2 [ffffb79140f73a18] crash_kexec at ffffffffaeda76ed
 #3 [ffffb79140f73a30] oops_end at ffffffffaec2658d
 #4 [ffffb79140f73a50] general_protection at ffffffffaf60111e
    [exception RIP: nfs_fattr_init+0x5]
    RIP: ffffffffc0c18265  RSP: ffffb79140f73b08  RFLAGS: 00010246
    RAX: 0000000000000000  RBX: ffff93dac304a800  RCX: 0000000000000000
    RDX: ffffb79140f73bb0  RSI: ffff93dadc8cbb40  RDI: d03ee11cfaf6bd50
    RBP: ffffb79140f73be8   R8: ffffffffc0691560   R9: 0000000000000006
    R10: ffff93db3ffd3df8  R11: 0000000000000000  R12: ffff93dac4040000
    R13: ffff93dac2848e00  R14: ffffb79140f73b60  R15: ffffb79140f73b30
    ORIG_RAX: ffffffffffffffff  CS: 0010  SS: 0018
 #5 [ffffb79140f73b08] _nfs41_proc_get_locations at ffffffffc0c73d53 [nfsv4]
 #6 [ffffb79140f73bf0] nfs4_proc_get_locations at ffffffffc0c83e90 [nfsv4]
 #7 [ffffb79140f73c60] nfs4_discover_trunking at ffffffffc0c83fb7 [nfsv4]
 #8 [ffffb79140f73cd8] nfs_probe_fsinfo at ffffffffc0c0f95f [nfs]
 #9 [ffffb79140f73da0] nfs_probe_server at ffffffffc0c1026a [nfs]
    RIP: 00007f6254fce26e  RSP: 00007ffc69496ac8  RFLAGS: 00000246
    RAX: ffffffffffffffda  RBX: 0000000000000000  RCX: 00007f6254fce26e
    RDX: 00005600220a82a0  RSI: 00005600220a64d0  RDI: 00005600220a6520
    RBP: 00007ffc69496c50   R8: 00005600220a8710   R9: 003035322e323231
    R10: 0000000000000000  R11: 0000000000000246  R12: 00007ffc69496c50
    R13: 00005600220a8440  R14: 0000000000000010  R15: 0000560020650ef9
    ORIG_RAX: 00000000000000a5  CS: 0033  SS: 002b

Fixes: 254a37718b3f ("NFSv4: Fix free of uninitialized nfs4_label on referral lookup.")
Signed-off-by: Scott Mayhew <smayhew@redhat.com>
Signed-off-by: Anna Schumaker <Anna.Schumaker@Netapp.com>