net: nfs: remove superfluous packed attribute

With GCC 9.2.1 net/nfs.c leads to multiple errors of type
address-of-packed-member.

net/nfs.c: In function ‘rpc_req’:
net/nfs.c:199:18: error: taking address of packed member of
‘struct rpc_t’ may result in an unaligned pointer value
[-Werror=address-of-packed-member]
  199 |  p = (uint32_t *)&(rpc_pkt.u.call.data);
      |                  ^~~~~~~~~~~~~~~~~~~~~~
net/nfs.c: In function ‘nfs_readlink_reply’:
net/nfs.c:631:46: error: taking address of packed member of
‘struct rpc_t’ may result in an unaligned pointer value
[-Werror=address-of-packed-member]
  631 |    nfs3_get_attributes_offset(rpc_pkt.u.reply.data);
      |                               ~~~~~~~~~~~~~~~^~~~~
  LD      drivers/block/built-in.o
net/nfs.c: In function ‘nfs_read_reply’:
net/nfs.c:692:46: error: taking address of packed member of
‘struct rpc_t’ may result in an unaligned pointer value
[-Werror=address-of-packed-member]
  692 |    nfs3_get_attributes_offset(rpc_pkt.u.reply.data);
      |                               ~~~~~~~~~~~~~~~^~~~~

struct rpc_t is only used as local variable. It is naturally packed. So
there is no need for the attribute packed.

Signed-off-by: Heinrich Schuchardt <xypron.glpk@gmx.de>
Reviewed-by: Bin Meng <bmeng.cn@gmail.com>
Acked-by: Joe Hershberger <joe.hershberger@ni.com>