extcon: Use tab instead of space for indentation

The extcon header file defines the functions which used the mismatched
indentation and used the space on some case. So, this patch clean-up
the indentation in order to improve the readbility.

And this patch changes the return value of extcon_get_extcon_dev()
because of maintaing the same value with extcon_get_edev_by_phandle().

Signed-off-by: Chanwoo Choi <cwchoi00@gmail.com>