Missing ATCA_MBEDTLS guard in atca_mbedtls_ecdsa.c

[AdityaHPatwardhan]

The file atca_mbedtls_ecdsa.c is missing the ATCA_MBEDTLS guard. (ref)
Without this the mbedtls code is still included even when ATCA_MBEDTLS is not defined.

Need to add it.

To Reproduce

Build the component with ATCA_MBEDTLS disabled.

Expected behavior

When ATCA_MBEDTLS is disabled, no mbedtls code should be required or pulled in.

[github-actions]

This issue has been marked as stale - please confirm the issue still exists with the latest version of the library and update the issue if it remains

[AdityaHPatwardhan]

Yes, the issue still exists