egl: Fix _eglPointerIsDereferencable() to ignore page residency

egl: Fix _eglPointerIsDereferencable() to ignore page residency

mincore() returns 0 on success, and -1 on failure.  The last parameter
is a vector of bytes with one entry for each page queried.  mincore
returns page residency information in the first bit of each byte in the
vector.

Residency doesn't actually matter when determining whether a pointer is
dereferenceable, so the output vector can be ignored.  What matters is
whether mincore succeeds. See:

  http://man7.org/linux/man-pages/man2/mincore.2.html

Signed-off-by: Miguel A. Vico <mvicomoya@nvidia.com>
Acked-by: Daniel Stone <daniels@collabora.com>
Reviewed-by: Emil Velikov <emil.velikov@collabora.com>