Fix TypeError in SPI/UART tests and correct frequency calculation

Description The current tests in tests/test_spi.py and tests/test_uart.py have two issues:

A typo in the constant name PWM_FERQUENCY.

A TypeError caused by attempting to perform arithmetic operations directly on the SPIMaster._frequency and UART._baudrate methods without calling them.

Proposed Solution

Rename the constant to PWM_FREQUENCY.

Fix the logic to correctly call the methods (e.g., SPIMaster._frequency()) to retrieve the integer value instead of using the method object itself.

Avoid hardcoding the frequency to 1000 to ensure tests remain meaningful.