Merge pull request #6434 from aabadie/petersen_typo

cpu/cc2538/include/periph_cpu.h

cpu/cc430/include/periph_cpu.h

cpu/k64f/include/cpu_conf.h

cpu/kinetis_common/include/periph_cpu.h

cpu/kw2x/include/cpu_conf.h

cpu/lpc1768/include/cpu_conf.h

cpu/lpc1768/include/periph_cpu.h

cpu/msp430fxyz/include/periph_cpu.h

cpu/native/include/periph_cpu.h

cpu/nrf51/include/cpu_conf.h

cpu/nrf51/include/periph_cpu.h

cpu/nrf52/include/cpu_conf.h

cpu/nrf52/include/periph_cpu.h

cpu/nrf5x_common/include/periph_cpu_common.h

cpu/sam0_common/include/periph_cpu_common.h

cpu/sam3/include/periph_cpu.h

cpu/samd21/include/periph_cpu.h

cpu/saml21/include/periph_cpu.h

cpu/stm32_common/include/periph_cpu_common.h

cpu/stm32f0/include/cpu_conf.h