mmc-utils: Fix 64-bit values redefinition

Some toolchains include asm-generic/int-l64.h from their asm/types.h
file for certain 64-bit architectures. This causes a conflict between
types like this one:

asm-generic/int-l64.h:28:25: error: conflicting types for '__s64'
 typedef __signed__ long __s64;
             ^
In file included from mmc.h:17:0,
         from mmc_cmds.c:30:
asm-generic/int-ll64.h:29:44: note: previous declaration of '__s64' was
here
 __extension__ typedef __signed__ long long __s64;

This patch has been submitted upstream.

Signed-off-by: Vicente Olivert Riera <Vincent.Riera@imgtec.com>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>