net: sunrpc: fix build errors when linux/phy*.h is removed from net/dsa.h

Removing linux/phy.h from net/dsa.h reveals a build error in the sunrpc
code:

net/sunrpc/xprtrdma/svc_rdma_backchannel.c: In function 'xprt_rdma_bc_put':
net/sunrpc/xprtrdma/svc_rdma_backchannel.c:277:2: error: implicit declaration of function 'module_put' [-Werror=implicit-function-declaration]
net/sunrpc/xprtrdma/svc_rdma_backchannel.c: In function 'xprt_setup_rdma_bc':
net/sunrpc/xprtrdma/svc_rdma_backchannel.c:348:7: error: implicit declaration of function 'try_module_get' [-Werror=implicit-function-declaration]

Fix this by adding linux/module.h to svc_rdma_backchannel.c

Signed-off-by: Russell King <rmk+kernel@armlinux.org.uk>
Acked-by: Anna Schumaker <Anna.Schumaker@Netapp.com>
Signed-off-by: David S. Miller <davem@davemloft.net>