nfsd: use correct format characters

When compiling with -Wformat, clang emits the following warnings:

fs/nfsd/flexfilelayout.c:120:27: warning: format specifies type 'unsigned
char' but the argument has type 'int' [-Wformat]
                         "%s.%hhu.%hhu", addr, port >> 8, port & 0xff);
                             ~~~~              ^~~~~~~~~
                             %d
fs/nfsd/flexfilelayout.c:120:38: warning: format specifies type 'unsigned
char' but the argument has type 'int' [-Wformat]
                         "%s.%hhu.%hhu", addr, port >> 8, port & 0xff);
                                  ~~~~                    ^~~~~~~~~~~
                                  %d

The types of these arguments are unconditionally defined, so this patch
updates the format character to the correct ones for ints and unsigned
ints.

Link: https://github.com/ClangBuiltLinux/linux/issues/378
Signed-off-by: Bill Wendling <morbo@google.com>
Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
Reviewed-by: Tom Haynes <loghyr@hammerspace.com>