reglib: fix memset usage

gcc-4.8 fails to compile reglib due to:

reglib.c:1133:22: error: argument to ‘sizeof’ in ‘memset’ call is
			 the same expression as the destination; did you mean
			 to dereference it? [-Werror=sizeof-pointer-memaccess]
  memset(rd, 0, sizeof(rd));
                      ^
reglib.c:1155:22: error: argument to ‘sizeof’ in... (same as above)

Signed-off-by: Christian Lamparter <chunkeey@googlemail.com>
Signed-off-by: Luis R. Rodriguez <mcgrof@do-not-panic.com>