Fix USE_SCSI_OP version of CD_SCSIUserOp
A fix from André Timmermans:
CD_SCSIUserOp is not working because of a bug in the SWI dispatch code.
In this code R11 is converted from a SWI offset nr into a softloadable driver opcode but when later the code checks if the driver implements the opcode or if it must call a local default implementation it compares R11 against SWI offset numbers (minus 1) instead of the driver opcodes. Per chance the number matches for the other opcodes but not for SCSIUserOp and so the softloadable driver is always called in this case even when there is no implementation for the opcode (like in CDFSSoftSCSI). Here is a patch to fix this.
Tested on BB-xM, fixes CD_SCSIUserOp not working with CDFSSoftSCSI.