fix(st-sdmmc): check transfer size before filling register

Fix MISRA C2012-10.3:
The value of an expression shall not be assigned to an object with
a narrower essential type or of a different essential type category.

Check buffer size is less than 4GB before casting the command argument.

Signed-off-by: Yann Gautier <yann.gautier@st.com>
Change-Id: Iac1afcfe905c99b22cb39dc4104d351b0e647e5d