scsi: core: Fix the scsi_set_resid() documentation

Because scsi_finish_command() subtracts the residual from the buffer
length, residual overflows must not be reported. Reflect this in the SCSI
documentation. See also commit 9237f04e12cc ("scsi: core: Fix
scsi_get/set_resid() interface")

Cc: Damien Le Moal <[e-mail]>
Cc: Hannes Reinecke <[e-mail]>
Cc: Douglas Gilbert <[e-mail]>
Cc: [e-mail]
Signed-off-by: Bart Van Assche <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Martin K. Petersen <[e-mail]>

Documentation/scsi/scsi_mid_low_api.rst

···
 		 - pointer to scsi_device object that this command is
                    associated with.
     resid
-		 - an LLD should set this signed integer to the requested
+		 - an LLD should set this unsigned integer to the requested
                    transfer length (i.e. 'request_bufflen') less the number
                    of bytes that are actually transferred. 'resid' is
                    preset to 0 so an LLD can ignore it if it cannot detect
-                   underruns (overruns should be rare). If possible an LLD
+                   underruns (overruns should not be reported). An LLD
                    should set 'resid' prior to invoking 'done'. The most
                    interesting case is data transfers from a SCSI target
                    device (e.g. READs) that underrun.