nrf_security: update description of MBEDTLS_SSL_EXTENDED_MASTER_SECRET

[hasheddan]

Fixes typos in the Kconfig description of
MBEDTLS_SSL_EXTENDED_MASTER_SECRET.

[CLAassistant]

All committers have signed the CLA.

[NordicBuilder]

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[mswarowsky]

LGTM

[NordicBuilder]

Test specification

CI/Jenkins/NRF

• Integration Platforms

CI/Jenkins/integration

Test Module	File based changes	Manually selected	West overwrite
test-fw-nrfconnect-chip	X
test-fw-nrfconnect-nrf_crypto	X
test-fw-nrfconnect-tfm	X
test-sdk-homekit	X

Detailed information of selected test modules

Note: This message is automatically posted and updated by the CI