Link against libcrypto, not all of openssl

In the previous build setup, libkmod.so would link to not just
libcrypto.so, but also libssl.so:

$ readelf -d /lib/libkmod.so | grep NEEDED
 0x0000000000000001 (NEEDED)             Shared library: [liblzma.so.5]
 0x0000000000000001 (NEEDED)             Shared library: [libz.so.1]
 0x0000000000000001 (NEEDED)             Shared library: [libssl.so.1.1]
 0x0000000000000001 (NEEDED)             Shared library: [libcrypto.so.1.1]
 0x0000000000000001 (NEEDED)             Shared library: [libc.so.6]

We don't need any symbols from libssl, though. This patch ensures that
we pass 'libcrypto' to pkgconfig rather than 'openssl', getting only the
library that we need:

$ readelf -d  ./libkmod/.libs/libkmod.so.2.3.4 | grep NEEDED
 0x0000000000000001 (NEEDED)             Shared library: [liblzma.so.5]
 0x0000000000000001 (NEEDED)             Shared library: [libz.so.1]
 0x0000000000000001 (NEEDED)             Shared library: [libcrypto.so.1.1]
 0x0000000000000001 (NEEDED)             Shared library: [libc.so.6]