The following warnings is fixed:
chip/sam_pwm.c:961:12: warning: unused variable 'regval' [-Wunused-variable]
961 | uint32_t regval;
chip/sam_serial.c: In function 'sam_dma_txavailable':
chip/sam_serial.c:2264:7: warning: unused variable 'rv' [-Wunused-variable]
2264 | int rv;
Signed-off-by: Michal Lenc <michallenc@seznam.cz>