drivers: flash: flash_mcux_flexspi_nor incorrectly handles border case

[Laczen]

Describe the bug

#84899 introduced input parameter checking for flash read operations.

The introduced check incorrectly handles the corner case where a read is performed of size 0 into a NULL array. The read fails with error code -EINVAL.

This introduces a difference between platforms when e.g. nvs_read is used to retrieve the size of an already stored element as reported in #86981.

To Reproduce

See #86981.

Expected behavior

No difference between platforms.

Logs and console output

See #86981.

Environment (please complete the following information):

See #86981.

[JordanYates]

I think you transposed some numbers in those issues, I doubt the reproduction case is a LoRa PR :)

[Laczen]

I think you transposed some numbers in those issues, I doubt the reproduction case is a LoRa PR :)

Updated, thanks :)

[dleach02]

@Laczen do you have a recommended fix?

[Laczen]

@Laczen do you have a recommended fix?

Return 0 when the read/write length is 0 before checking the read/write buffer.

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