Fix some whitespace quoting errors

Author: Evan Benn

pico_setup.sh

@@ -147,7 +147,7 @@ fail() {
 
 validate_git_repo() {
     # tests that the given relative path exists and is a git repo
-    git -C ${TARGET_DIR}/${1} status >& /dev/null || fail
+    git -C "${TARGET_DIR}/${1}" status >& /dev/null || fail
 }
 
 validate_toolchain_linux() {
@@ -365,13 +365,13 @@ validate_pico_examples() {
     validate_git_repo pico-examples
 
     # test that blink is built
-    test -f ${TARGET_DIR}/pico-examples/build/blink/blink.uf2 || fail
+    test -f "${TARGET_DIR}/pico-examples/build/blink/blink.uf2" || fail
 
     # test that hello_serial is built
-    test -f ${TARGET_DIR}/pico-examples/build/hello_world/serial/hello_serial.uf2 || fail
+    test -f "${TARGET_DIR}/pico-examples/build/hello_world/serial/hello_serial.uf2" || fail
 
     # test that hello_usb is built
-    test -f ${TARGET_DIR}/pico-examples/build/hello_world/usb/hello_usb.uf2 || fail
+    test -f "${TARGET_DIR}/pico-examples/build/hello_world/usb/hello_usb.uf2" || fail
 }
 
 validate_pico_playground() {