Fix error being reported twice
Fix error being reported twice

If 'stlink_v1_open_inner' returns NULL then 'stlink_v1_open' prints
to stderr thus there is no need for the former one to print it also.

This removes 'Error: could not open stlink device' being printed
twice.

trigrass2/stlink,chaosAD/stlink,fedorcomander/stlink,braincorp/stlink,simonjwright/stlink,fedorcomander/stlink,swegener/stlink,chaosAD/stlink,swegener/stlink,gtalusan/stlink,simonjwright/stlink,trigrass2/stlink,gtalusan/stlink,braincorp/stlink