ice: Fix some null pointer dereference issues in ice_ptp.c

devm_kasprintf() returns a pointer to dynamically allocated memory
which can be NULL upon failure.

Fixes: d938a8cc

 ("ice: Auxbus devices & driver for E822 TS")
Cc: Kunwu Chan <kunwu.chan@hotmail.com>
Suggested-by: Przemek Kitszel <przemyslaw.kitszel@intel.com>
Signed-off-by: Kunwu Chan <chentao@kylinos.cn>
Reviewed-by: Przemek Kitszel <przemyslaw.kitszel@intel.com>
Reviewed-by: Simon Horman <horms@kernel.org>
Tested-by: Pucha Himasekhar Reddy <himasekharx.reddy.pucha@intel.com> (A Contingent worker at Intel)
Signed-off-by: Tony Nguyen <anthony.l.nguyen@intel.com>