pcm: Fix up some compile warnings that show up under some sim builds
firmware/pcm_mixer.c:36:35: warning: conversion from ‘long unsigned int’ to ‘unsigned int’ changes value from ‘18446744073709551615’ to ‘4294967295’ [-Woverflow]
36 | static unsigned int mixer_sampr = -1UL;
|
firmware/pcm_mixer.c:269:21: warning: comparison is always false due to limited range of data type [-Wtype-limits]
269 | if (mixer_sampr == -1UL)
| ^~
So drop the 'L' and everything is peachy.
Change-Id: I9440d3300931be229c6c4b01bdc1d09b55c34d88