nfs-utils: Fix C aliasing rules violation in nfs_getrpccaller()

Squelch compiler warnings reported with -Wextra:

In file included from statd.c:24:
../../support/include/rpcmisc.h: In function nfs_getrpccaller_in:
../../support/include/rpcmisc.h:58: warning: dereferencing type-punned
pointer might break strict-aliasing rules
../../support/include/rpcmisc.h: In function nfs_getrpccaller:
../../support/include/rpcmisc.h:63: warning: dereferencing type-punned
pointer might break strict-aliasing rules

Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
Signed-off-by: Steve Dickson <steved@redhat.com>