[2020.07] cpu/stm32: use correct CMSIS header for stm32f103xe line

[aabadie]

Contribution description

This PR replace the CMSIS header used for stm32f103xe cpu line by the valid one. In 2020.07, the CMSIS for stm32f101xe was used by mistake in #14143.

Testing procedure

• Green Murdock
• Tests on iotlab-m3 should still work

Issues/PRs references

fixes #15041

[fjmolinas]

ACK, tested and it works. I'm somehow surprised this didn't break earlier:

2020-09-18 18:15:23,489 # help
2020-09-18 18:15:23,491 # Command              Description
2020-09-18 18:15:23,492 # ---------------------------------------
2020-09-18 18:15:23,494 # udp                  send data over UDP and listen on UDP ports
2020-09-18 18:15:23,495 # reboot               Reboot the node
2020-09-18 18:15:23,497 # version              Prints current RIOT_VERSION
2020-09-18 18:15:23,498 # pm                   interact with layered PM subsystem
2020-09-18 18:15:23,500 # ps                   Prints information about running threads.
2020-09-18 18:15:23,500 # ping6                Ping via ICMPv6
2020-09-18 18:15:23,500 # ping                 Ping via ICMPv6
2020-09-18 18:15:23,501 # random_init          initializes the PRNG
2020-09-18 18:15:23,505 # random_get           returns 32 bit of pseudo randomness
2020-09-18 18:15:23,506 # nib                  Configure neighbor information base
2020-09-18 18:15:23,506 # ifconfig             Configure network interfaces
2020-09-18 18:15:23,507 # rpl                  rpl configuration tool ('rpl help' for more information)
2020-09-18 18:15:23,508 # 6ctx                 6LoWPAN context configuration tool
>

[miri64]

I removed the check from the release branch. @bergzand, remind me to reactivate it, once the 2020.10-branch is there.