sd: lower log level for boot message

This log message does not need to be repeated 10 times at the INFO level
when the same information is provided after all the retries are done:
```
<inf> sd: Legacy card detected, no CMD8 support
<inf> sd: Legacy card detected, no CMD8 support
<inf> sd: Legacy card detected, no CMD8 support
<inf> sd: Legacy card detected, no CMD8 support
<inf> sd: Legacy card detected, no CMD8 support
<inf> sd: Legacy card detected, no CMD8 support
<inf> sd: Legacy card detected, no CMD8 support
<inf> sd: Legacy card detected, no CMD8 support
<inf> sd: Legacy card detected, no CMD8 support
<inf> sd: Legacy card detected, no CMD8 support
<inf> sd: Legacy card detected, no CMD8 support
<inf> sd: Card does not support CMD8, assuming legacy card
```
to
```
<inf> sd: Card does not support CMD8, assuming legacy card
```

Signed-off-by: Jordan Yates <jordan@embeint.com>