scsi: target: core: Constify enabled() in struct target_opcode_descriptor

Constify the first argument of the enabled() function in struct
target_opcode_descriptor.

This is the first step in order to constify struct
target_opcode_descriptor.

Signed-off-by: Christophe JAILLET <christophe.jaillet@wanadoo.fr>
Link: https://lore.kernel.org/r/4290cf1dbe100c1b1edf2ede5e5aef19b04ee7f2.1747592774.git.christophe.jaillet@wanadoo.fr


Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>