net: airoha: Fix MBI_RX_AGE_SEL_MASK definition

Fix copy-paste error in MBI_RX_AGE_SEL_MASK macro definition

Fixes: 23020f04

 ("net: airoha: Introduce ethernet support for EN7581 SoC")
Signed-off-by: Lorenzo Bianconi <lorenzo@kernel.org>
Reviewed-by: Simon Horman <horms@kernel.org>
Link: https://patch.msgid.link/d27d0465be1bff3369e886e5f10c4d37fefc4934.1721419930.git.lorenzo@kernel.org


Signed-off-by: Paolo Abeni <pabeni@redhat.com>