Replace "four bytes" with "two bytes" in macro documentation
Replace "four bytes" with "two bytes" in macro documentation

When writing the documentation 4 bytes was written instead of 2 for
MBEDTLS_UINT16_LE

Signed-off-by: Joe Subbiani <58338b749ceb75cc139988a3309cc9c135482ffd@arm.com>

Mbed-TLS/mbedtls,ARMmbed/mbedtls,NXPmicro/mbedtls,NXPmicro/mbedtls,ARMmbed/mbedtls,ARMmbed/mbedtls,ARMmbed/mbedtls,Mbed-TLS/mbedtls,Mbed-TLS/mbedtls,Mbed-TLS/mbedtls,NXPmicro/mbedtls,NXPmicro/mbedtls