staging: greybus: Inline pwm_chip_to_gb_pwm_chip()

Convert 'pwm_chip_to_gb_pwm_chip' from a macro to a static
inline function, to make the relevant types apparent in the
definition and to benefit from the type checking performed by
the compiler at call sites.

Signed-off-by: Sumitra Sharma <sumitraartsy@gmail.com>
Link: https://lore.kernel.org/r/20230326064519.GA179449@sumitra.com


Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>