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

cmd/zdb/zdb.c

@@ -1991,7 +1991,7 @@ dump_ddt_log(ddt_t *ddt)
 				c += strlcpy(&flagstr[c], " UNKNOWN",
 				    sizeof (flagstr) - c);
 			flagstr[1] = '[';
-			flagstr[c++] = ']';
+			flagstr[c] = ']';
 		}
 
 		uint64_t count = avl_numnodes(&ddl->ddl_tree);
@@ -8800,7 +8800,6 @@ zdb_decompress_block(abd_t *pabd, void *buf, void *lbuf, uint64_t lsize,
 	(void) buf;
 	uint64_t orig_lsize = lsize;
 	boolean_t tryzle = ((getenv("ZDB_NO_ZLE") == NULL));
-	boolean_t found = B_FALSE;
 	/*
 	 * We don't know how the data was compressed, so just try
 	 * every decompress function at every inflated blocksize.
@@ -8843,20 +8842,19 @@ zdb_decompress_block(abd_t *pabd, void *buf, void *lbuf, uint64_t lsize,
 		for (cfuncp = cfuncs; *cfuncp; cfuncp++) {
 			if (try_decompress_block(pabd, lsize, psize, flags,
 			    *cfuncp, lbuf, lbuf2)) {
-				found = B_TRUE;
+				tryzle = B_FALSE;
 				break;
 			}
 		}
 		if (*cfuncp != 0)
 			break;
 	}
-	if (!found && tryzle) {
+	if (tryzle) {
 		for (lsize = orig_lsize; lsize <= maxlsize;
 		    lsize += SPA_MINBLOCKSIZE) {
 			if (try_decompress_block(pabd, lsize, psize, flags,
 			    ZIO_COMPRESS_ZLE, lbuf, lbuf2)) {
 				*cfuncp = ZIO_COMPRESS_ZLE;
-				found = B_TRUE;
 				break;
 			}
 		}