build: Fix GCRYPT_HWF_MODULES.

* configure.ac (GCRYPT_HWF_MODULES): Add libgcrypt_la- prefix.

Before this change "make distcheck" fails because
src/.deps/hwf-x86.Plo remains. Note that the distclean entry for the
file is libgcrypt_la-hwf-x86.Plo.

• Signed-off-by: NIIBE Yutaka <gniibe@fsij.org>