Fix tswap size

p in this case is uint32_t *

e1/e2 are unsigned ints initialized from arithmetics performed on
unsigned longs

The mistake was, probably, never noticed due to the absence of any
big endian linux-user host. The types e1/e2 and p begs the quesiton
why this function takes longs at all.

git-svn-id: svn://svn.savannah.nongnu.org/qemu/trunk@5036 c046a42c-6fe2-441c-8c8c-71466251a162