m25p80: avoid out of bounds accesses

m25p80: avoid out of bounds accesses

s->cur_addr can be made to point outside s->storage, either by
writing a value >= 128 to s->ear (because s->ear * MAX_3BYTES_SIZE
is a signed integer and sign-extends into the 64-bit cur_addr),
or just by writing an address beyond the size of the flash being
emulated.  Avoid the sign extension to make the code cleaner, and
on top of that mask s->cur_addr to s->size.

Signed-off-by: Paolo Bonzini <[email protected]>
Reviewed-by: Cédric Le Goater <[email protected]>
Signed-off-by: Cédric Le Goater <[email protected]>
Message-id: 1467138270[email protected]
Reviewed by: Marcin Krzeminski <[email protected]>
Signed-off-by: Cédric Le Goater <[email protected]>
Signed-off-by: Peter Maydell <[email protected]>