package/openssl: fix coding style

Currently, openssl defines three conditional hooks, but two do not
follow our coding rules:
  - for PRE_CONFIGURE, the hook is defined in the if-block, but
    the _HOOK variable is always set
  - for POST_INSTALL_TARGET, the hook is always defined, but the
    _HOOK variable is set in the if-block

Fix that:
  - define the hook in the if-block
  - assign the _HOOK variable in the if-block

At the same time, get rid of extra empty lines that make it more
difficult to read.

Signed-off-by: "Yann E. MORIN" <yann.morin.1998@free.fr>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>