ARM: dts: msm: adjust virtual HOME/BACK key map for msm8953 qrd

The virtual keys HOME/BACK are incorrectly defined
for msm8953 qrd. Exchange the positions of these three virtual
keys for a correct operation of the device.

Change-Id: I272326d06ee990c4b7409126fa22d85556ab384d
Signed-off-by: Mao Li <maol@codeaurora.org>