scripts/get-developers: correct type of patches argument

scripts/get-developers: correct type of patches argument

Current type for 'patches' argument is str. It supposed to only
contain names of files.

If we specify FileType as type, then we don't need to open file ourself
and it allows script to read patch from standard input as well.

e.g.
$ git show -1 | ./support/scripts/get-developers -

Cc: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
Signed-off-by: Rahul Bedarkar <rahul.bedarkar@imgtec.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>