panfrost: Remove duplicate variable ret

Fix defect reported by Coverity Scan.

Evaluation order violation (EVALUATION_ORDER)
write_write_typo:
In ret = ret = ({...; drmIoctl(panfrost_device_fd(dev), 3221775434UL, &args);}),
ret is written twice with the same value.

Fixes: e9aedfe508 ("panfrost: Support JM context creation and destruction")
Signed-off-by: Vinson Lee <vlee@freedesktop.org>
Reviewed-by: Erik Faye-Lund <erik.faye-lund@collabora.com>
Reviewed-by: Boris Brezillon <boris.brezillon@collabora.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/37708>

src/gallium/drivers/panfrost/pan_jm.c

@@ -1057,9 +1057,9 @@ GENX(jm_init_context)(struct panfrost_context *ctx)
       .priority = prio,
    };
 
-   int ret = ret = pan_kmod_ioctl(panfrost_device_fd(dev),
-                                  DRM_IOCTL_PANFROST_JM_CTX_CREATE,
-                                  &args);
+   int ret = pan_kmod_ioctl(panfrost_device_fd(dev),
+                            DRM_IOCTL_PANFROST_JM_CTX_CREATE,
+                            &args);
    if (ret)
       return -1;