drivers: flash-nxp-s32-qspi: ignore flash operations with zero size

The current shim driver for flash-nxp-s32-qspi returns invalid error
when handling write, erase operations with zero size.
This issue causes the failure of the tests/subsys/settings/fcb/.
Updated to ignore the flash operations with zero size instead of.

Signed-off-by: Cong Nguyen Huu <cong.nguyenhuu@nxp.com>