media: amphion: Fix a build error: 'fmt' undeclared

Delete the call to vpu_helper_find_format() in the
vdec_check_source_change() function, due to the commit
18d582f5

 ("media: amphion: tell and handle contiguous
and non contiguous format") back port, this part of the
code has not been deleted.

Signed-off-by: Xiaolei Wang <xiaolei.wang@windriver.com>
Signed-off-by: Bruce Ashfield <bruce.ashfield@gmail.com>