rtl8187: Fixed section mismatch in rtl8187_dev.c

When CONFIG_HOTPLUG=n the following error occures on vmlinux linkage:

`.exit.text' referenced in section `.data' of drivers/built-in.o:
defined in discarded section `.exit.text' of drivers/built-in.o

'rtl8187_disconnect' function marked as __devexit isn't compiled with no
hotplug support. Added __devexit_p macros to fix the problem.

Signed-off-by: Ihar Hrachyshka <ihar.hrachyshka@promwad.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>