regedit_valuelist.c: Coverity fix; Initialize a variable.

regedit_valuelist.c: Coverity fix; Initialize a variable.

The <tmp> variable is tested at the end of the function to determine the
return value, but <tmp> is never initialized and there are conditions
under which it may be tested before a value is set.

This patch initializes <tmp> to NULL, which means that WERR_NOMEM will
be returned if the registry lookups fail.

CID:  1168007

Signed-off-by: Christopher R. Hertel (crh) <crh@samba.org>
Reviewed-by: Jeremy Allison <jra@samba.org>