doc: point to the STM32MP1 directory

Markdown links reports error 429, try to avoid this.

Signed-off-by: Frederic Pillon <[email protected]>

Author: fpistm

README.md

@@ -210,8 +210,8 @@ User can add a STM32 based board following this [wiki](https://github.com/stm32d
 
 | Status | Device(s) | Name | Release | Notes |
 | :----: | :-------: | ---- | :-----: | :---- |
-| :green_heart:  | STM32MP157A | [STM32MP157A-DK1](https://www.st.com/en/evaluation-tools/stm32mp157a-dk1.html) | *1.8.0* | See [the documentation](https://github.com/stm32duino/Arduino_Core_STM32/tree/main/variants/STM32MP1xx/MP153AAC_MP153CAC_MP153DAC_MP153FAC_MP157AAC_MP157CAC_MP157DAC_MP157FAC/README.md) to use this board|
-| :green_heart:  | STM32MP157C | [STM32MP157C-DK2](https://www.st.com/en/evaluation-tools/stm32mp157c-dk2.html) | *1.8.0* | See [the documentation](https://github.com/stm32duino/Arduino_Core_STM32/tree/main/variants/STM32MP1xx/MP153AAC_MP153CAC_MP153DAC_MP153FAC_MP157AAC_MP157CAC_MP157DAC_MP157FAC/README.md) to use this board|
+| :green_heart:  | STM32MP157A | [STM32MP157A-DK1](https://www.st.com/en/evaluation-tools/stm32mp157a-dk1.html) | *1.8.0* | See [the documentation](https://github.com/stm32duino/Arduino_Core_STM32/tree/main/variants/STM32MP1xx/MP153AAC_MP153CAC_MP153DAC_MP153FAC_MP157AAC_MP157CAC_MP157DAC_MP157FAC) to use this board|
+| :green_heart:  | STM32MP157C | [STM32MP157C-DK2](https://www.st.com/en/evaluation-tools/stm32mp157c-dk2.html) | *1.8.0* | See [the documentation](https://github.com/stm32duino/Arduino_Core_STM32/tree/main/variants/STM32MP1xx/MP153AAC_MP153CAC_MP153DAC_MP153FAC_MP157AAC_MP157CAC_MP157DAC_MP157FAC) to use this board|
 
 ### Generic STM32C0 boards