net/avp: fix 32-bit meson builds

net/avp: fix 32-bit meson builds

When compiling with meson, extra warnings are enabled about casting from
integers to different size pointers. This triggers an error in AVP as the
addition of the offset to the pointer address causes the result to be a
64-bit integer which doesn't fit a 32-bit pointer. The fix here is to
explicitly indicate that the offset is of type "uintptr_t" which prevents
any promotion which would cause errors.

Fixes: c0ad584222b5 ("net/avp: add device initialization")

Signed-off-by: Bruce Richardson <bruce.richardson@intel.com>
Acked-by: Allain Legacy <allain.legacy@windriver.com>
Acked-by: Hemant Agrawal <hemant.agrawal@nxp.com>