net: liquidio: fix clang-specific W=1 build warnings

When compiling with clang-18 and W=1, I've noticed the following
warnings:

drivers/net/ethernet/cavium/liquidio/cn23xx_pf_device.c:1493:16: warning: cast
from 'void (*)(struct octeon_device *, struct octeon_mbox_cmd *, void *)' to
'octeon_mbox_callback_t' (aka 'void (*)(void *, void *, void *)') converts to
incompatible function type [-Wcast-function-type-strict]
 1493 |         mbox_cmd.fn = (octeon_mbox_callback_t)cn23xx_get_vf_stats_callback;
      |                       ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

and:

drivers/net/ethernet/cavium/liquidio/cn23xx_vf_device.c:432:16: warning: cast
from 'void (*)(struct octeon_device *, struct octeon_mbox_cmd *, void *)' to
'octeon_mbox_callback_t' (aka 'void (*)(void *, void *, void *)') converts to
incompatible function type [-Wcast-function-type-strict]
  432 |         mbox_cmd.fn = (octeon_mbox_callback_t)octeon_pfvf_hs_callback;
      |                       ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Fix both of the above by adjusting 'octeon_mbox_callback_t' to match actual
callback definitions (at the cost of adding an extra forward declaration).
Signed-off-by: Dmitry Antipov <dmantipov@yandex.ru>
Reviewed-by: Simon Horman <horms@kernel.org>
Link: https://lore.kernel.org/r/20240111162432.124014-1-dmantipov@yandex.ruSigned-off-by: Jakub Kicinski <kuba@kernel.org>

drivers/net/ethernet/cavium/liquidio/cn23xx_pf_device.c

@@ -1490,7 +1490,7 @@ int cn23xx_get_vf_stats(struct octeon_device *oct, int vfidx,
 	mbox_cmd.q_no = vfidx * oct->sriov_info.rings_per_vf;
 	mbox_cmd.recv_len = 0;
 	mbox_cmd.recv_status = 0;
-	mbox_cmd.fn = (octeon_mbox_callback_t)cn23xx_get_vf_stats_callback;
+	mbox_cmd.fn = cn23xx_get_vf_stats_callback;
 	ctx.stats = stats;
 	atomic_set(&ctx.status, 0);
 	mbox_cmd.fn_arg = (void *)&ctx;

drivers/net/ethernet/cavium/liquidio/cn23xx_vf_device.c

@@ -429,7 +429,7 @@ int cn23xx_octeon_pfvf_handshake(struct octeon_device *oct)
 	mbox_cmd.q_no = 0;
 	mbox_cmd.recv_len = 0;
 	mbox_cmd.recv_status = 0;
-	mbox_cmd.fn = (octeon_mbox_callback_t)octeon_pfvf_hs_callback;
+	mbox_cmd.fn = octeon_pfvf_hs_callback;
 	mbox_cmd.fn_arg = &status;
 
 	octeon_mbox_write(oct, &mbox_cmd);

drivers/net/ethernet/cavium/liquidio/octeon_mailbox.h

@@ -57,7 +57,10 @@ union octeon_mbox_message {
 	} s;
 };
 
-typedef void (*octeon_mbox_callback_t)(void *, void *, void *);
+struct octeon_mbox_cmd;
+
+typedef void (*octeon_mbox_callback_t)(struct octeon_device *,
+				       struct octeon_mbox_cmd *, void *);
 
 struct octeon_mbox_cmd {
 	union octeon_mbox_message msg;