media: lirc: LIRC_GET_REC_RESOLUTION should return microseconds

Since commit e8f48188 ("[media] lirc: advertise
LIRC_CAN_GET_REC_RESOLUTION and improve") lircd uses the ioctl
LIRC_GET_REC_RESOLUTION to determine the shortest pulse or space that
the hardware can detect. This breaks decoding in lirc because lircd
expects the answer in microseconds, but nanoseconds is returned.

Cc: <stable@vger.kernel.org> # v2.6.36+
Reported-by: Derek <user.vdr@gmail.com>
Tested-by: Derek <user.vdr@gmail.com>
Signed-off-by: Sean Young <sean@mess.org>
Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>