crypto: cavium - cpt_bind_vq_to_grp could return an error code

cpt_bind_vq_to_grp() could return an error code. However, it currently
returns a u8. This produce the static checker warning.

drivers/crypto/cavium/cpt/cptpf_mbox.c:70 cpt_bind_vq_to_grp() warn: signedness bug returning '(-22)'

Reported-by: Dan Carpenter <[e-mail]>
Signed-off-by: George Cherian <[e-mail]>
Signed-off-by: Herbert Xu <[e-mail]>

drivers/crypto/cavium/cpt/cptpf_mbox.c

···
 	cpt_write_csr64(cpt->reg_base, CPTX_PF_QX_CTL(0, vf), pf_qx_ctl.u);
 }
 
-static u8 cpt_bind_vq_to_grp(struct cpt_device *cpt, u8 q, u8 grp)
+static int cpt_bind_vq_to_grp(struct cpt_device *cpt, u8 q, u8 grp)
 {
 	struct microcode *mcode = cpt->mcode;
 	union cptx_pf_qx_ctl pf_qx_ctl;
···
 {
 	struct cpt_vf_info *vfx = &cpt->vfinfo[vf];
 	struct cpt_mbox mbx = {};
-	u8 vftype;
+	int vftype;
 	struct device *dev = &cpt->pdev->dev;
 	/*
 	 * MBOX[0] contains msg