We can't assume <asm/errno.h> to be available on non-Linux hosts.
Furthermore, errno constants values aren't fixed and passing them
to libc perror(3)/strerror (3) would yield wrong results.
Fix this by using the standard <errno.h> header instead.

Signed-off-by: Ahmad Fatoum <a.fatoum@pengutronix.de>
Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>