ubi-tests: fm_param: Replace 'fm_auto' with 'fm_autoconvert'

ubi-tests: fm_param: Replace 'fm_auto' with 'fm_autoconvert'

The value of fm_param should be 'fm_autoconvert' rather than 'fm_auto' when
fastmap is supported by kernel. Currently, following verbose will appear in
dmesg when fm_param is set to 'fm_auto':

  ubi: unknown parameter 'fm_auto' ignored

This patch replace 'fm_auto' with 'fm_autoconvert' for fm_param, so ubi
kernel module can receive correct parameters.

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Signed-off-by: Zhihao Cheng <chengzhihao1@huawei.com>
Signed-off-by: David Oberhollenzer <david.oberhollenzer@sigma-star.at>