rxrpc: avoid clang -Wuninitialized warning

clang produces a false-positive warning as it fails to notice
that "lost = true" implies that "ret" is initialized:

net/rxrpc/output.c:402:6: error: variable 'ret' is used uninitialized whenever 'if' condition is true [-Werror,-Wsometimes-uninitialized]
        if (lost)
            ^~~~
net/rxrpc/output.c:437:6: note: uninitialized use occurs here
        if (ret >= 0) {
            ^~~
net/rxrpc/output.c:402:2: note: remove the 'if' if its condition is always false
        if (lost)
        ^~~~~~~~~
net/rxrpc/output.c:339:9: note: initialize the variable 'ret' to silence this warning
        int ret, opt;
               ^
                = 0

Rearrange the code to make that more obvious and avoid the warning.

Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Reviewed-by: Nathan Chancellor <natechancellor@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>