periph_spi/main.c: Adapt to recent RIOT changes of spi_acquire()

[MarcelStenzel]

spi_acquire() was changed to a void function with https://github.com/RIOT-OS/RIOT/pull/15902 This adapts to these changes and the spi tests are able be build again.

[riot-hil-bot]

HiL Test Results	PASS	FAIL	SKIP
27	3	0

  ❌ samr34-xpro <(1 fail build)

``` tests/periph_spi: build fail ```

  😬 nrf52dk (1 fail flash)

``` tests/periph_spi: flash fail ```

  😬 frdm-k64f (1 fail flash)

``` tests/periph_spi: flash fail ```

  ✅ frdm-k22f

``` tests/periph_spi: pass ```

  ✅ nucleo-f091rc

``` tests/periph_spi: pass ```

  ✅ nucleo-f303re

``` tests/periph_spi: pass ```

  ✅ same54-xpro

``` tests/periph_spi: pass ```

  ✅ nucleo-f767zi

``` tests/periph_spi: pass ```

  ✅ nucleo-l152re

``` tests/periph_spi: pass ```

  ✅ arduino-mega2560

``` tests/periph_spi: pass ```

  ✅ nucleo-l432kc

``` tests/periph_spi: pass ```

  ✅ hifive1b

``` tests/periph_spi: pass ```

  ✅ saml10-xpro

``` tests/periph_spi: pass ```

  ✅ saml11-xpro

``` tests/periph_spi: pass ```

  ✅ samr30-xpro

``` tests/periph_spi: pass ```

  ✅ samr21-xpro

``` tests/periph_spi: pass ```

  ✅ saml21-xpro

``` tests/periph_spi: pass ```

  ✅ remote-revb

``` tests/periph_spi: pass ```

  ✅ nucleo-f207zg

``` tests/periph_spi: pass ```

  ✅ nucleo-l073rz

``` tests/periph_spi: pass ```

  ✅ slstk3401a

``` tests/periph_spi: pass ```

  ✅ nucleo-g474re

``` tests/periph_spi: pass ```

  ✅ nucleo-f411re

``` tests/periph_spi: pass ```

  ✅ nucleo-f103rb

``` tests/periph_spi: pass ```

  ✅ frdm-kw41z

``` tests/periph_spi: pass ```

  ✅ esp32-wroom-32

``` tests/periph_spi: pass ```

  ✅ z1

``` tests/periph_spi: pass ```

  ✅ arduino-due

``` tests/periph_spi: pass ```

  ✅ slstk3400a

``` tests/periph_spi: pass ```

  ✅ stk3200

``` tests/periph_spi: pass ```

[MrKevinWeiss]

Hmmm I think we need different testing metrics for Robot tests vs RIOT tests. There should be more failing... Either way the outcome looks good (the comments are wrong though).