Save code size by calling get_type only once
Save code size by calling get_type only once

This is an external function, so in the absence of link-time
optimisation (LTO) the compiler can't know anything about it and has to
call it the number of times it's called in the source code.

This only matters for pk_ec, but change pk_rsa as well for the sake of
uniformity.

Signed-off-by: Manuel Pégourié-Gonnard <4ba0d615aeeda88e422ca8fba28fe2938485facf@arm.com>

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