tcl/memory: fix syntax errors

Using a command in an expression requires a bracketed command
substitution.

These syntax errors were caught by tclint v0.2.5
(https://github.com/nmoroze/tclint):

```
tclint tcl/memory.tcl | grep "syntax error"
```

Change-Id: I510d46222f4fb02d6ef73121b231d5b2df77e5c0
Signed-off-by: Noah Moroze <noahmoroze@gmail.com>
Reviewed-on: https://review.openocd.org/c/openocd/+/8279
Reviewed-by: Antonio Borneo <borneo.antonio@gmail.com>
Tested-by: jenkins

tcl/memory.tcl

@@ -66,10 +66,10 @@ proc iswithin { ADDRESS BASE LEN } {
 proc address_info { ADDRESS } {
 
     foreach WHERE { FLASH RAM MMREGS XMEM UNKNOWN } {
-	if { info exists $WHERE } {
+	if { [info exists $WHERE] } {
 	    set lmt [set N_[set WHERE]]
 	    for { set region 0 } { $region < $lmt } { incr region } {
-		if { iswithin $ADDRESS $WHERE($region,BASE) $WHERE($region,LEN) } {
+		if { [iswithin $ADDRESS $WHERE($region,BASE) $WHERE($region,LEN)] } {
 		    return  "$WHERE $region";
 		}
 	    }