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
eecba412cd