nfsd: nfs4xdr.c do-while is not a compound statement

The WRITEMEM macro produces sparse warnings of the form:
fs/nfsd/nfs4xdr.c:2668:2: warning: do-while statement is not a compound statement
Signed-off-by: NHarvey Harrison <harvey.harrison@gmail.com>
Cc: Benny Halevy <bhalevy@panasas.com>
Signed-off-by: NJ. Bruce Fields <bfields@citi.umich.edu>

fs/nfsd/nfs4xdr.c

@@ -1160,11 +1160,11 @@ nfsd4_decode_compound(struct nfsd4_compoundargs *argp)
 	*p++ = htonl((u32)((n) >> 32));				\
 	*p++ = htonl((u32)(n));					\
 } while (0)
-#define WRITEMEM(ptr,nbytes)     do if (nbytes > 0) {		\
+#define WRITEMEM(ptr,nbytes)     do { if (nbytes > 0) {		\
 	*(p + XDR_QUADLEN(nbytes) -1) = 0;                      \
 	memcpy(p, ptr, nbytes);					\
 	p += XDR_QUADLEN(nbytes);				\
-} while (0)
+}} while (0)
 #define WRITECINFO(c)		do {				\
 	*p++ = htonl(c.atomic);					\
 	*p++ = htonl(c.before_ctime_sec);				\