input: sensors: read 16-bit output data in continuous mode

Read 16-bit output data in continuous measurement mode to use
the same sensitivity adjustments as single measurement mode.
This allows the driver to report proper magnitude to userspace
in continuous measurement mode.

Change-Id: I3f3fa46e98f703bae9328df7bdb2150cb843bba8
Signed-off-by: Kiran Raparthy <krapar@codeaurora.org>