drivers: clock_control: fix typo in STM32H7* clock init

Correct typo in STM32H7 HSI clock calibration directives introduced
in commit 6b167f2596f3 ("drivers: clock_control: add calibration for
h7 pllx_hsi") that currently has no functionnal impact but is worth
to be fixed for consistency.

No functional change,

Fixes: 6b167f2596f3171c0923fcc97b7974d0218dc8a4
Signed-off-by: Etienne Carriere <etienne.carriere@st.com>
1 file changed