linux/zvol_os: fix SET_ERROR with negative return codes

SET_ERROR is our facility for tracking errors internally. The negation
is to match the what the kernel expects from us. Thus, the negation
should happen outside of the SET_ERROR.

Reviewed-by: Tony Hutter <hutter2@llnl.gov>
Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Sponsored-by: Klara, Inc.
Sponsored-by: Wasabi Technology, Inc.
Signed-off-by: Rob Norris <rob.norris@klarasystems.com>
Closes #16364