octeontx2-pf: handle otx2_mbox_get_rsp errors in otx2_dmac_flt.c

[ Upstream commit f5b942e6 ]

Add error pointer checks after calling otx2_mbox_get_rsp().

Fixes: 79d2be38 ("octeontx2-pf: offload DMAC filters to CGX/RPM block")
Fixes: fa5e0ccb ("octeontx2-pf: Add support for exact match table.")
Signed-off-by: Dipendra Khadka <kdipendra88@gmail.com>
Reviewed-by: Simon Horman <horms@kernel.org>
Signed-off-by: Andrew Lunn <andrew@lunn.ch>
Signed-off-by: Sasha Levin <sashal@kernel.org>