time: fix gcc warnings on MIPS64

Commit 8dfafdde introduced
new gcc warnings on MIPS64:

time.c: In function 'tick_to_time':
time.c:59:2: warning: comparison of distinct pointer types lacks a cast [enabled by default]
time.c:59:2: warning: passing argument 1 of '__div64_32' from incompatible pointer type [enabled by default]
In file included from time.c:10:0:
./u-boot-mips/include/div64.h:22:17: note: expected 'uint64_t *' but argument is of type 'long long unsigned int *'
time.c: In function 'usec_to_tick':
time.c:76:2: warning: comparison of distinct pointer types lacks a cast [enabled by default]
time.c:76:2: warning: passing argument 1 of '__div64_32' from incompatible pointer type [enabled by default]
In file included from time.c:10:0:
./u-boot-mips/include/div64.h:22:17: note: expected 'uint64_t *' but argument is of type 'long long unsigned int *'

Signed-off-by: Daniel Schwierzeck <daniel.schwierzeck@gmail.com>