cavs: (cosmetic) clean up and simplification of intc_cavs.c

1. don't use "inline" in .c, let the compiler decide
2. remove superfluous parentheses
3. simplify a function by directly returning the result of a boolean
operation

Signed-off-by: Guennadi Liakhovetski <guennadi.liakhovetski@linux.intel.com>