devtools: fix checkpatch for filename with space

If the patch filename or the temporary file path have a space
in their name, the script checkpatches.sh does not work.
The variables for the filenames must be enclosed in quotes
in order to preserve spaces.

Fixes: 4bec48184e33 ("devtools: add checks for ABI symbol addition")

Signed-off-by: Thomas Monjalon <thomas@monjalon.net>
Acked-by: Neil Horman <nhorman@tuxdriver.com>