soc: aspeed: Fix snoop_file_poll()'s return type

snoop_file_poll() is defined as returning 'unsigned int' but the
.poll method is declared as returning '__poll_t', a bitwise type.

Fix this by using the proper return type and using the EPOLL
constants instead of the POLL ones, as required for __poll_t.

Link: https://lore.kernel.org/r/20191121051851.268726-1-joel@jms.id.au


Fixes: 3772e5da ("drivers/misc: Aspeed LPC snoop output using misc chardev")
Signed-off-by: Luc Van Oostenryck <luc.vanoostenryck@gmail.com>
Reviewed-by: Joel Stanley <joel@jms.id.au>
Reviewed-by: Andrew Jeffery <andrew@aj.id.au>
Signed-off-by: Joel Stanley <joel@jms.id.au>
Signed-off-by: Olof Johansson <olof@lixom.net>