doc: st: fix `nucleo_h533re` documentation

1. Changing default ADC sens line for ch0 on PA0
- `adc1` was documented to be sensing ch14 on PB1.
- This seems impossible because of a conflict between ch14
and UART2.
- `adc1` node is not defined in the board's DTS.

2. Set SPI1 NSS pin to PA4
- hardware NSS signal was documented to output on PC9.
- PC9 cannot be assigned as HW NSS for SPI1.
- HW NSS on SPI1 is by default on PA4, and remapeable to PA15.

3. Update number of UART lines available
- There are a total of 7 U(S)ARTs available on this board.

Signed-off-by: Alex Fabre <alex.fabre@rtone.fr>