Fix typos in cmd/

Reviewed-by: Ryan Moeller <ryan@ixsystems.com>
Reviewed-by: Richard Laager <rlaager@wiktel.com>
Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: Andrea Gelmini <andrea.gelmini@gelma.net>
Closes #9234

cmd/zstreamdump/zstreamdump.c

@@ -197,7 +197,7 @@ print_block(char *buf, int length)
 }
 
 /*
- * Print an array of bytes to stdout as hexidecimal characters. str must
+ * Print an array of bytes to stdout as hexadecimal characters. str must
  * have buf_len * 2 + 1 bytes of space.
  */
 static void