fix(fdt-wrappers): use correct prototypes

fix(fdt-wrappers): use correct prototypes

These issues were triggered by sparse tool:
common/fdt_wrappers.c:209:36:
 warning: incorrect type in assignment (different base types)
  expected unsigned long long [usertype]
  got restricted fdt64_t
common/fdt_wrappers.c:211:36:
 warning: incorrect type in assignment (different base types)
  expected unsigned int [usertype]
  got restricted fdt32_t
common/fdt_wrappers.c:401:45:
 warning: incorrect type in argument 1 (different base types)
  expected restricted fdt32_t const [usertype] *prop
  got unsigned int const [usertype] *value
common/fdt_wrappers.c:402:52:
 warning: incorrect type in argument 1 (different base types)
  expected restricted fdt32_t const [usertype] *prop
  got unsigned int const [usertype] *
common/fdt_wrappers.c:404:66:
 warning: incorrect type in argument 1 (different base types)
  expected restricted fdt32_t const [usertype] *prop
  got unsigned int const [usertype] *

Signed-off-by: Yann Gautier <yann.gautier@st.com>
Change-Id: I32067607cd4da1897f0ce5d8e1e2d51e044ab815