net: sparx5: fix function return type to match actual type

Function returns error integer, not bool.

Does not have any impact on functionality.

Reported-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Casper Andersson <casper.casan@gmail.com>
Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Link: https://lore.kernel.org/r/20220906065815.3856323-1-casper.casan@gmail.com
Signed-off-by: Paolo Abeni <pabeni@redhat.com>