In clang version 21.1 and later the -Wimplicit-enum-enum-cast warning
option has been introduced. This warning is enabled by default and can
be used to catch .queuecommand() implementations that return another
value than 0 or one of the SCSI_MLQUEUE_* constants. Hence this patch
that changes the return type of the .queuecommand() implementations from
'int' into 'enum scsi_qc_status'. No functionality has been changed.