contrib/initrd hooks: properly quote @LIBFETCH_SONAME@

Bullseye shellcheck picks these up as SC2140, and it's right!
@LIBFETCH_SONAME@ is already quoted, so dracut had

"$d/"libcurl.so.4""

and i-t had

""libcurl.so.4""

Partially reverts 34eef3e9a7a74d24a59d016051d547afc55dbaa0 (#12760),
which broke this

Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: Ahelenia Ziemiańska <nabijaczleweli@nabijaczleweli.xyz>
Closes #12835