avcodec/tiff: do not use photometric to detect pix_fmt

They should match but they do not always
Fixes assertion failure
no testcase with unmodified source available

Signed-off-by: Michael Niedermayer <michaelni@gmx.at>
avcodec/tiff: Check that pix_fmt is a yuv variant for TIFF_PHOTOMETRIC_YCBCR

Signed-off-by: Michael Niedermayer <michaelni@gmx.at>