zephyr: Fix README
Fix the path for running gdb.
BRANCH=None
TEST=Ran gdb
Tested-by: Jeremy Bettis
@@ -44,7 +44,7 @@ Build the test
Then run gdb
```
-(chroot) gdb build/zephyr/test/drivers/build-singleimage/zephyr/zephyr.exe
+(chroot) gdb build/zephyr/test-drivers/build-singleimage/zephyr/zephyr.exe
# Set breakpoints, run, etc.
```
