fix(PeriphDrivers): Fix UART DMA Callbacks for UART1+

[Jake-Carter]

Description

Fixes #998

As the internal UART state struct was only initialized per used UART instance, attempting to use UART1 (or higher) with DMA auto handlers would never trigger the user's callback functions. The state struct's DMA channel values would be initialized to 0 instead of -1, which the drivers would assume was a valid channel acquisition.

This PR fixes the bug by initializing the UART state array correctly.

Checklist Before Requesting Review

• [ ] PR Title follows correct guidelines.
• [ ] Description of changes and all other relevant information.
• [ ] (Optional) Link any related GitHub issues using a keyword
• [ ] (Optional) Provide info on any relevant functional testing/validation. For API changes or significant features, this is not optional.

[EricB-ADI]

I recommend designated initializers instead of runtime. That way you don't need any runtime operations after and need to manage more global state.

#define NUM_MEMBERS 4

typedef struct  
{
    int32_t a , b, c;
}example_t;

example_t test[NUM_MEMBERS] = {
    [0 ... NUM_MEMBERS - 1] = {.a = -1, .b = -1, .c = -1}
};

[Jake-Carter]

I recommend designated initializers instead of runtime. That way you don't need any runtime operations after and need to manage more global state.

#define NUM_MEMBERS 4

typedef struct  
{
    int32_t a , b, c;
}example_t;

example_t test[NUM_MEMBERS] = {
    [0 ... NUM_MEMBERS - 1] = {.a = -1, .b = -1, .c = -1}
};

Thanks @EricB-ADI, I was looking for this type of syntax. Just updated the PR

[Jake-Carter]

@EricB-ADI ready for final review