rtl8187: fix compile warning

ANAPARAM3 register, defined in the rtl818x common register
struct, is accessed as 16bit by rtl8187se and as 8bit by rtl8187b.
Since I have no documentation about this, I can only stick to
the reference code and to what is known to work.

This issue has been addressed by a patch from Larry Finger
that introduces an "union", in the register struct.
In my last patch-set I applied it on the register struct, but
I forget to update rtl8187 driver too.
This patch does it.

Suggested-by: Larry Finger <Larry.Finger@lwfinger.net> [ Original patch ]
Signed-off-by: Andrea Merello <andrea.merello@gmail.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>