cpu/efm32: pwm_init errors are zeros

[chrysn]

Contribution description

pwm_init is documented to return 0 on errors, and has an unsigned return value.

EFM32's initialization function returned negative values, which through implicit casting become 0xffffffff or 0xfffffffe, which are successful by the documentation.

This makes all the EFM32 error paths return 0 as they should.

Also, it fixes a variable name and the corresponding error message that used to talk of "initiation" (which would be the start of a process) rather than "initialization" (which is a process that is completed before something else can happen).

Testing procedure

• on stk3700, tests/periph_pwm, run init 0 0 10 1000 / set 0 0 500
• The init used to respond with "The pwm frequency is set to 4294967294", and the set does nothing.
• The init now responds with "Error: device is not initiatedinitialized". The set still does nothing, but then one doesn't expect it to any more.

(But really, looking at the patch and the docs should suffice).

Issues/PRs references

By-catch from testing the Rust wrappers provided by @Remmirad at RIOT-OS/rust-riot-wrappers#38

[riot-ci]

Murdock results

✔️ PASSED

6c8d1eb tests/periph_pwm: wording fix, s/initiate/initialize/

Success	Failures	Total	Runtime
6882	0	6882	10m:11s

Artifacts

• Documentation preview

[benpicco]

bors merge

[chrysn]

Thanks for the quick ACK.

By the way, I did also check the other pwm.c implementations: They're all good -- they either return 0, or they just assert that their parameters are right. (One might argue for either behavior to be better, but that's not this issue, and frankly, I don't think it matters much).

[bors]

Build succeeded:

• Murdock
• static-tests
• tools-build-success