everywhere: misc unnecessary var init/update

These are all cases where we initialise or update a variable, and then
never use it. None of them particularly matter, as the compiler should
optimise them all away during dead store elimination, but some static
analysers complain about them and they are extra work for casual readers
to follow, so worth removing.

Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Reviewed-by: Alexander Motin <mav@FreeBSD.org>
Signed-off-by: Rob Norris <robn@despairlabs.com>
Sponsored-by: https://despairlabs.com/sponsor/
Closes #17551

lib/libspl/include/umem.h

@@ -102,7 +102,7 @@ static inline void *
 umem_alloc_aligned(size_t size, size_t align, int flags)
 {
 	void *ptr = NULL;
-	int rc = EINVAL;
+	int rc;
 
 	do {
 		rc = posix_memalign(&ptr, align, size);

lib/libzfs/libzfs_crypto.c

@@ -584,7 +584,7 @@ get_key_material_https(libzfs_handle_t *hdl, const char *uri,
 		goto end;
 	}
 
-	int kfd = -1;
+	int kfd;
 #ifdef O_TMPFILE
 	kfd = open(getenv("TMPDIR") ?: "/tmp",
 	    O_RDWR | O_TMPFILE | O_EXCL | O_CLOEXEC, 0600);

lib/libzfs/libzfs_pool.c

@@ -896,7 +896,7 @@ int
 zpool_set_prop(zpool_handle_t *zhp, const char *propname, const char *propval)
 {
 	zfs_cmd_t zc = {"\0"};
-	int ret = -1;
+	int ret;
 	char errbuf[ERRBUFLEN];
 	nvlist_t *nvl = NULL;
 	nvlist_t *realprops;
@@ -4310,7 +4310,7 @@ zpool_set_guid(zpool_handle_t *zhp, const uint64_t *guid)
 	libzfs_handle_t *hdl = zhp->zpool_hdl;
 	nvlist_t *nvl = NULL;
 	zfs_cmd_t zc = {"\0"};
-	int error = -1;
+	int error;
 
 	if (guid != NULL) {
 		if (nvlist_alloc(&nvl, NV_UNIQUE_NAME, 0) != 0)

lib/libzpool/kernel.c

@@ -1067,8 +1067,8 @@ zvol_rename_minors(spa_t *spa, const char *oldname, const char *newname,
 int
 zfs_file_open(const char *path, int flags, int mode, zfs_file_t **fpp)
 {
-	int fd = -1;
-	int dump_fd = -1;
+	int fd;
+	int dump_fd;
 	int err;
 	int old_umask = 0;
 	zfs_file_t *fp;