scsi: target: core: Remove unused 'prod_len' variable

clang with W=1 reports:

drivers/target/target_core_spc.c:229:6: error: variable
  'prod_len' set but not used [-Werror,-Wunused-but-set-variable]
        u32 prod_len;
            ^
This variable is not used so remove it.

Signed-off-by: Tom Rix <trix@redhat.com>
Link: https://lore.kernel.org/r/20230329132421.1809362-1-trix@redhat.com
Reviewed-by: Chaitanya Kulkarni <kch@nvidia.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>

Author: Tom Rix

drivers/target/target_core_spc.c

@@ -226,7 +226,6 @@ spc_emulate_evpd_83(struct se_cmd *cmd, unsigned char *buf)
 	struct t10_alua_lu_gp_member *lu_gp_mem;
 	struct t10_alua_tg_pt_gp *tg_pt_gp;
 	unsigned char *prod = &dev->t10_wwn.model[0];
-	u32 prod_len;
 	u32 off = 0;
 	u16 len = 0, id_len;
 
@@ -267,10 +266,6 @@ spc_emulate_evpd_83(struct se_cmd *cmd, unsigned char *buf)
 	 * T10 Vendor Identifier Page, see spc4r17 section 7.7.3.4
 	 */
 	id_len = 8; /* For Vendor field */
-	prod_len = 4; /* For VPD Header */
-	prod_len += 8; /* For Vendor field */
-	prod_len += strlen(prod);
-	prod_len++; /* For : */
 
 	if (dev->dev_flags & DF_EMULATED_VPD_UNIT_SERIAL)
 		id_len += sprintf(&buf[off+12], "%s:%s", prod,