devtool: Fix the wrong variable in srcuri_entry

devtool crashes when running "update-recipe" and append changes on the recipe.
"$ devtool update-recipe -a <layer> <recipe>"
Traceback (most recent call last):
...
File "/ovss/ovss_quanta/poky/scripts/lib/devtool/standard.py", line 1636, in srcuri_entry
    return 'file://%s%s

' % (basepath, paramstr)
                            ^^^^^^^^
NameError: cannot access free variable 'basepath' where it is not associated with a value in enclosing scope

The input variable 'fname' should have the same meaning as the variable 'basepath'.
Modify the 'fname' to 'basepath' and solve the issue.

Signed-off-by: Charlie Wu <chiachiwu@google.com>
Signed-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>