cortex-m: warnings: Address -Wextra warnings

`#defines` do NOT sepecify a type. They will either adopt a native
system type or type of the value that was passed into the expression.
This can lead to warnings such as, "warning: comparison of integer
expressions of different signedness: 'uint32_t' {aka 'unsigned int'}
and 'int' [-Wsign-compare]".

By casting expressions, such as `MAX_TICKS` to `k_ticks_t`, we can
force the appropriate types and resolve these warnings.

Signed-off-by: Zachary J. Fields <zachary_fields@yahoo.com>