net: sparx5: Fix initialization of variables on stack

The variables 'res' inside the functions sparx5_ptp_get_1ppm and
sparx5_ptp_get_nominal_value was not initialized. So in case of the default
case of the switch after, it would return an uninitialized variable.
This makes also the clang builds to failed.

Fixes: 0933bd04 ("net: sparx5: Add support for ptp clocks")
Signed-off-by: Horatiu Vultur <horatiu.vultur@microchip.com>
Link: https://lore.kernel.org/r/20220304140918.3356873-1-horatiu.vultur@microchip.com


Signed-off-by: Jakub Kicinski <kuba@kernel.org>